C8888 Nanochemistry Nanomaterials 1 Jiri Pinkas Office A12/224 Phone 549496493 Email: jpinkas@chemi.muni.cz Ph.D. level course Prerequsite C7780 Inorganic Materials Chemistry Course grading: Select a topic concerning nanochemistry and prepare: Presentation - 30 min (20 %) Written term paper - min 5 pages (80 %) Au nanoparticles C8888 Nanochemistry Time Plan for Spring 2019 Nanomaterials 2 Feb 18 - Lecture 1 Feb 26 - no lecture Mar 5 - Lecture 2 Mar 12 - Lecture 3 Mar 19 - Lecture 4 - Think of a topic for your paper Mar 26 - Lecture 5 - Send me a 1-page abstract of your paper Apr 2 - Lecture 6 - Final topic approval Apr 9 - work on a paper Apr 16 - work on a paper Apr 23 - work on a paper Apr 30 - 3 presentations May 7 - 3 presentations May 14 - no lecture - Hand in your term paper Nanomaterials 3 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 4 Nanoscopic Scales Nanomaterials 5 Nanoparticles 1 – 100 nm Traditional materials > 1 m Nanoscopic Materials 1 nm = 109 m 1 nm = 10 Å Nanomaterials 6 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 7 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 8 “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 9 Room at the Bottom Manipulation atom-by-atom Nanomaterials 10 STM Scanning Tunelling Microscopy 1982 Binning and Rohrer Nobel Prize 1986 Nanoscale Writing Nanomaterials 11 STM positioned Xe atoms on Ni crystal, 5 nm letters Manipulation atom-by-atom AFM Nanomaterials 12 Atomic Force Microscopy 1986 Binnig, Quate, and Gerber a method allowing a variety of non-conducting surfaces to be imaged and characterized at the atomic level the detection of forces between an observed sample surface and a sharp tip located at the end of a cantilever AFM Nanomaterials 13 Nanomaterials 14 Nanoscale Writing Nanomaterials 15 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 16 Nanoscopic Size The largest known bacterium Thiomargarita namibiensis - 100-750 microns 1 – 100 nm Nanomaterials 17 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 18 The Nano-Family 1-D structures (2-D confinement): • Nanowires • Nanorods • Nanotubes • Nanofibers Nanomaterials 19 Electrospinning Nanofibers Nanomaterials 20 The Nano-Family 2-D structures (1-D confinement): • Thin films - CVD, ALD • Planar quantum wells • Superlattices • Graphene • SAM Nanomaterials 21 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) Nanoscopic Behavior of Materials Nanomaterials 22 • Surface Effects • Quantum Confinement Effects Differences between bulk and nanoscale materials Nanomaterials 23 Decreasing grain size = Increasing volume fraction of grain boundaries (50% for 3 nm particles) Surface Effects Ru particle diameter 2.9 nm Nanomaterials 24 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 25 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 Close Packed Atoms Nanomaterials 26 Close Packed Atoms Nanomaterials 27 Nanomaterials 28 Surface Effects Atoms at surfaces - fewer neighbors than atoms in the bulk = lower coordination number - stronger and shorter bonds - unsatisfied bonds - dangling 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 Dangling Bonds Nanomaterials 29 • Empty orbital • 1-e orbital • 2-e orbital Nanomaterials 30 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 31 Graphite shells Nanomaterials 32 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 is the bulk value? Nanomaterials 33 Surface Effects Atom binding (vaporization) energies lower in nanoparticles, fewer neighbors to keep atoms from escaping Plasticity of nanocrystalline ceramics Surface Effects in Alloys Nanomaterials 34 Alloys: Core-shell Janus Random mixture Au-Pt 586 atoms Nanomaterials 35 ICP-OES: Ag 50.3 mol%, EDS: Ag 62.5 mol% ICP-OES: Ag 68.8 mol%, EDS: Ag 84.2 mol% Transmission Electron Microscopy Energy Dispersive X-ray Spectroscopy Effects of Synthesis Nanomaterials 36 AgCu 413 Ag 393 Cu 569 Localized Surface Plasmon Resonance (LSPR) Nanomaterials 37 Faraday’s colloidal solution of gold Localized Surface Plasmon Resonance (LSPR) Nanomaterials 38 Nanomaterials 39 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 = depression of melting point of nanoparticles. Nanomaterials 40 Melting Point and Enthalpy Depression Nanocalorimetry of Sn nanoparticles Tm bulk = 232 C Hm bulk = 58.9 J/g Nanomaterials 41 Melting Point and Enthalpy Depression Nanocalorimetry of Sn nanoparticles Nanomaterials 42 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 43 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 44 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 45 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 46 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 47 Surface Effects Reduction in particle size • Metal particles usually exhibit a lattice contraction • Oxide particles exhibit a lattice expansion YIG = Y3Fe5O12 Nanomaterials 48 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 49 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 50  Finite-size effects MO to Band transition Quantum Confinement Effects Physical and chemical properties depend on the size !! Quantum Size Effects Nanomaterials 51 Band gap dependency on the nanoparticle size Nanomaterials 52 Quantum Size Effects Metals Semiconductors Nanomaterials 53 Metal-to-Insulator Transition Nanomaterials 54 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 55 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 56 Electrical Conductivity Particle size Bulk value Relativeconductivity Nanomaterials 57 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 58 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 59 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 60 Bohr Radii Quantum confinement - particles must be smaller than the Bohr radius of the electron-hole pair Nanomaterials 61 Quantum Confinement Effects Optical properties nc-TiO2 is transparent - applications? Blue shift in optical spectra of TiO2 nanoparticles