■ Nanoscopic Materials Atoms/ Nanoscale Condensed Molecules Particles Matter 1 125 70,000 6x106 oo N° Atoms 1 ^ 10 100 oc Diameter(nm) Quantum / Solid State Chemistry m Physics - Nanomaterials i Nanostructural Materials "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. Nanomaterials 2 Room at the Bottom What I want to talk about is the problem of manipulating and controlling things on a small scale ... As soon as I mention this, people tell me about miniaturization, and how far it has progressed today. They tell me about electric motors that are the size of the nail on your small finger. And there is a device on the market, they tell me, by which you can write the Lord's Prayer on the head of a pin. But that's nothing? that's the most primitive, halting step in the direction I intend to discuss. It's a staggeringly small world that is below. In the year 2000, when they look back at this age, they will wonder why it was not until the year 1960 that anybody began seriously to move in this direction...... Prof. Richard Feynman in "There's plenty of room at the bottom", lecture delivered at the annual meeting of the APS, Caltech, 29 December, 1959. Nanomaterials 3 Nanoscale Writing Jen NanolithOgraphy AFMTlp Wrltthg direction V„vrt ltanl*cu* Nanoscale writing with an AFM (Mirkin et al.) 60 ran R'S soon os T rnent Ton th"s. people te! I me aboa's m f niutur Fiiat-*on, and how ^ar T* ^os programed "t'Otk^ Tl t*L| i-t1!1 nv ubout eT^ctrTc mo'-rTi that th$> cf ^he naH vi ijcw -j-nuM r"nj^r. Rr.J ij t-re a dtvlcir 0*1 ^hp? n1 irk^t. ^hey * t-f I ttip. '.-.'h^ih ljcj '.jr;t e the Lord's Prayer cm T,he head of 0 p7i. B^tr * hnj-t, ' $ riotrino^ shot's t W w»Cn*ft pr r rr*'^. fwfr. h^l* :njj *;*cp fm w d'r^^Jo^ T friend d'sci-^i. It it e bt ajcjaer 1 ng ' y sma1 f wor'd tho-t Is bete*..*. In trie uear en they lo'A bock at th'o -jo*?, they wortaW -jh^ it- Utfj* rvoT unto I the ye^ir 1^0 %hat anybody t^gar 5r?r"o^sfy to rnouc in this dJrei.Vion. 400 nm Pr chard P. Feynrr-ar., Nanomaterials 4 ■ Nanoscopic Materials Size is another variable to change physical and chemical properties Each physical property or fenomenon has a characteristic length When particle size is comparable to the characteristic length, property start to depend on th^fize1^ 5 Nanoscopic Materials 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 Nanomaterials 6 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. Nanomaterials Nanoscopic Materials Nanoscale regime Size 1 - 100 nm (traditional materials > 1 ^m) Nanoscopic Materials Nanoparticles 1 - 100 nm Traditional materials > 1 |jm 1 nm = 10-9 m 1 nm = 10 A Nanomaterials 8 STM Scanning Tunelling Microscopy Binning and Rohrer Nobel 1986 Nanomaterials 9 The largest known bacterium - Thiomargarita namibiensis - 100-750 microns Nanomaterials 11 Microns to Nanometers - Biological/Chemical/Atomic i^&S AFM 1 |jm x 1 |jm InAs on GaAs/InP Nanomater1a1s 13 The Nano-Family 1-D structures (2-D confinement): ApUinďalypUniA^M ASH kw* if n lamtubiMianiaargTBH' MbnnHlUia m Or. P. M AJiyaa) . . (9Mna hm Or. P. kLAJtym) , r JN anomatenals 15 EIektrospinning Nanomaterials 16 ■ ■ .. The Nano-Family 2-D structures (1-D confinement): • Thin films • Planar quantum wells • Superlattices • Graphene •SAM Si/Ge/Si/Ge Superlattice < 100 nm NanOmuiviiuij 17 Coherence Length a) XRD patterns of iron oxide nanocrystals of 4, 6, 8, 9, 10, 11, 12, 13, and 15 nm OH) (440) —f— —I— ■10 (311) f-i> —i-i-i-i-i-i-i 32 33 34 35 3E 37 3ft 39 2 Bulk Atoms ■ / / 4* y A i Surface Atoms 10 l-r 15 2C Nanomaterials 2* 34 Particle Size(nm) 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 F r 2 1 1 r 3 r F g 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 > Mossbauer spectroscopy, quadrupole splitting distribution broadened >Diffusivity enhanced by up to 20 orders of magnitude !! Si > 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 have fewer neighbours than atoms in the bulk Lower coordination and 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 surface-to-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 neighbours, lower coordination, unsatisfied (dangling) bonds B = Atoms close to surface (several layers) - deformation of coordination sphere, distorted bond distances and angles C = Bulk atoms - not present in particles below 2 nm Nanomaterials 23 coordination number Surface Effects N -U3 Calculated mean coordination number as a function of inverse radius, represented by N-1/3 for Mg clusters (triangles = icosahedra, squares = decahedra, diamonds = hcp Nanomaterials 24 Surface Effects Atom binding (vaporization) energies lower in nanoparticles, fewer neighbors to keep atoms from escaping Plasticity of nanocrystalline ceramics Nanomaterials 25 ■ ■ .. Melting Point Depression AT = Tbmblk - Tm (r) 2T bulk m Hbmdk pr m good sinterability >high catalytic activity > difficult handling > adsorption of gases and impurities >poor compressibility Nanomaterials 44 ■ ■ .. Nanoscopic Materials Nanostructured materials = nonequilibrium character NANO -particles, crystals, powders -films, patterned films -wires, rods, tubes -dots >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 Nanomaterials 45 Bottom-up Synthesis: Atom Up NANOSTRUCTURAL MATERIALS Bottom-up Synthesis 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 Nanomaterials 47 ■ ■ .. NANOSTRUCTURAL MATERIALS Bottom-up Synthesis 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 77 to 300 K 180 0 8 Co + 2 B2O3 Co + H2 + B2H6 TiCl4 + 2 NaBH4 -> TiB2 + 2 NaCl + 2 HCl + H2 MXn + n NR4[BEt3H]-► M + NR4X + n BEt3 + n/2 H2 mixed-metal particles M = group 6 to 11; n = 2,3; X = Cl, Br Nanomaterials 50 NANOSTRUCTURAL MATERIALS Bottom-up Synthesis 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 Nanomaterials 51 Bottom-up Synthesis SH Nanomaterials 52 TEM micrograph of hexagonal arrays of thiolized Pd nanocrystals: a) 2.5 nm, octane thiol b) 3.2 nm, octane thiol Nanomaterials 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 55 NANOSTRUCTURAL MATERIALS Alkali Metal Reduction in dry anaerobic diglyme, THF, ethers, xylene NiCl2 + 2 K Ni + 2 KCl AlCL + 3 K — Al + 3 KCl Reduction by Glycols or Hydrazine "Organically solvated metals" K + Nanomaterials Mg 56 Alkalide Reduction 13 K+(15-crown-5)2Na- + 6 FeCl3 + 2CBr4 THF -30 °C 2 Fe3C (nano) + 13 K(15-crown-5)2Cl043Br057 + 13 NaCl Anealed at 950 °C / 4 h Fe3C: 2 - 15 nm Nanomaterials 57 Conducting carbon wires Acrylonitrile introduced into MCM-41 (3 nm diam. channels) Radical polymerization Pyrolysis gives carbon filaments NANOSTRUCTURAL MATERIALS Bottom-up Synthesis ^ 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)32+ reduction of Ru(III) Nanomaterials 58 ■ ■ .. NANOSTRUCTURAL MATERIALS Bottom-up Synthesis $t Gel or Polymer Matrices * Sol-Gel Method Aerogels, supercritical drying $C 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? Nanomaterials 59 ■ ■ .. NANOSTRUCTURAL MATERIALS Inverse Micelles Bottom-up Synthesis Bottom-up Synthesis Phase Control [NnBu4]2[Fe4S4(SPh)4] Bottom-up Synthesis 180oC in octylamine 200 oC in dodecylamine pyrrhotite Fe7S8 greigite Fe3S4 thiospinel, the sulfide analogue of magnetite 62 .30 nrn i Polymerie Nanoparticles from Rapid Expansion of Supercritical Fluid Solution Nanomaterials 63 Polymerie Nanoparticles from Rapid Expansion of Supercritical Fluid Solution Nanomaterials 64 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 |im) 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 CorrrailKi NANOSTRUCTURAL MATERIALS Properties on Nanostruetured Materials ® Metallic behavior 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 Nanomaterials 66 ■ ■ .. LaMer mechanism Supersaturated solution Burst of nucleation Slow growth of particles without additional nucleation Separation of nucleation and growth Nanomaterials 67 Watzky-Finke mechanism Slow continuous nucleation Fast autocatalytic surface growth Nanomaterials 68 Seed-mediated mechanism Au nanoclusters as seeds Bi, Sn, In, Au, Fe, Fe3O4 Nanomaterials 69 Other mechanisms Digestive rippening Surfactant exchange Nanomaterials 70 Thermal Decomposition of Precursors Fe(CO)5 350 oC, 1 h _ oleic acid trioctylamine *- Fe 350 oC, 1 h 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 O OH Nanomaterials 71 Top-down Synthesis: Bulk Down 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 72 a) XRD patterns of iron oxide nanocrystals of 4, 6, 8, 9, 10, 11, 12, 13, and 15 nm (311) (440) -r- ■10 2? Nanomaterials 15 nm (311) 32 33 34 35 3E 37 38 39 26-•* 73 Nanocatalysis Morphologies of bimetallic nanoparticles Metal H □ Nanomaterials 74 Nanocatalysis Polymers used as metal NP supports for catalysis H2 + ^ř^OH = Pd° no no particle OH + H2 O = pď Nanomaterials a Pd° nanoparticle 75 Nanocatalysis Catalysis by nanoparticles encapsulated in PAMAM or PPI dendrimers DiPdv^Rhy3! Nanomaterials 76 Nanocatalysis Asymmetric heterogeneous catalysis on nanoparticles Nanomaterials 77 ■ ■ .. Hollow Nanoparticles Nanomaterials 7S ■ ■ .. Applications Destruction of dangerous organic compounds (organophosphates - VX, chlorinated - PCB) Nanomaterials 79 Nanoengine Nanomotor funguje díky katalýze (viz obr.) U platinové části tyčinky se štěpí peroxid vodíku (H2O2) na kyslík (O2) a protony (H+). Přebytečné elektrony se přesunují k stříbrozlaté části tyčinky, čímž nastartují redukční reakci H2O2 a protonů a vzniká voda. Uvolnění kyslíku a vody vytváří slabé proudění, které žene nanotyčinku kapalinou, a to platinovou částí napřed. Slovo Fliessrichtung na obrázku znamená směr proudění. Slitina zlata a stříbra se postará o to, že se k ní elektrony přesunují rychleji. Tím se urychlí i rozpad pohonné látky a tyčinky jsou o to rychlejší. 150 mikrometrů za sekundu Josepha Wanga z Kalifornské univerzity v San Diegu a Arizonské státní univerzity Nanomaterials 81