Dimension-Properties Interplay Brilliant, Transparent Metallic lusture Opaque Black, Fibrous Black Shiny Crystals Mohs Hardness 10 1-2 1-1.2 20W/cmK 25 6000 High Melting point Lubricant Unusual Superconductor Electrical Behaviour (10-40 K) 1 High Axial Ratio Nanostructures One Dimensional Architectures Role of Dimensionality / / M. M r ^p í / f V ■y 8 r 2' # vW v i O 3D * E 'E 'E 2D ID Energy OD ^E 3 Role of Dimensionality 3D: E = 2D: E = 2m 2m kj*+ky2+kx2\ **2+*>2+Kf 1 D: E = 2m ft \2 r „\ ft V. L J OD: E = 2m f 'v ft L ^2 / "'I ^ J \ L) V **} ft^ L ^=1,2,3 i^ =1,2,3 W =1,2,3 4 ID Nanostructures ^A^T\^ c—c—c—o c-c DNA Molecular Wire The Nano World HI 250 lim Poly {ethylene oxide) Collagen Fibrils Characteristics of ID Nanostructures Properties Small Light weight Novel 1 -D properties High aspect ratio High surface area Potential applications Interconnects Novel Probes Multifunctional Hierarchical alignment Building blocks for devices 6 Potential of Nanowires Electron Transport 'Nano-cables' Core-shell Superlattice AFM & STM Tips Surface Modification 7 Effect of Confinement 1 10 100 1000 10000 100000 Diameter (A) The band gap increases with decreasing diameter (quantum confinement) 8 Carbon Nanotubes • Discovered by Iijima (1991, NEC) • Rolled up sheet of graphene • Capped at the ends with half a fullerene Carbon Nanotubes Single Walled Nanotube ( SWNT) • Single atomic layer wall • Diameter of 1 - 5 nm • Length several microns Multi Walled Nanotube ( MWNT) • Concentric tubes ca. 50 in number • Inner diameters : 1.5 - 15 nm • Outer diameters : 2.5 - 30 nm 10 CNTs: Properties and Potential Electronic: Bandgap Eg - 1/d Magnetic: Anisotropic magn. susceptibility X-1-^ Mechanical: Young's Modulus ~ 1 TPa (SWNT) 1.25 TPa (MWNT) (Steel: 230 GPa) Thermal: Conductivity 6000 W/m.K (Copper 400 W/m.K) Defect-free (n,m) SWNTs with open ends A) A metallic conducting (10,10) tube (armchair) B) a chiral, semiconducting (12,7) tube, C) a conducting (15,0) tube (zigzag). The armchair (A) and zigzag (C) tubes are achiral. All the (n,n) armchair tubes are metallic, whilst this is only the case with chiral or zigzag tubes if (n-m)/3 is a whole number, otherwise, they are semiconductors 12 A bundle of (10,10) nanotubes held together with strong 71-71-stacking interactions 13 a 2D graphite layer the lattice vectors ax and a2 the roll-up vector Ch= na1+ma2 Achiral tubes exhibit roll-up vectors derived from (n,0) (zigzag) or (n,n) (armchair). The translation vector T is parallel to the tube axis and defines the ID unit cell. The rectangle represents an unrolled unit cell, defined by T and Ch In this example, (n,m)=(4,2) 14 Functionalization possibilities for SWNTs A) defect-group functionalization B) covalent sidewall functionalization C) noncovalent exohedral functionalization with Surfactants D) noncovalent exohedral functionalization with polymers E) endohedral functionalization with C60 15 Interconnect IBM Transistor A h.lĽĽlíodc 7\ iMSÜ Nanomanipulator LTŮ ľ m ZK Bio-Sensor V**vs m*. Wrf NU-i. _i__i__i__i__i__i__i__■__i__i__i__.__i__i__i__i__i_____■__i__i_ i» ?ir -m ^w NU Chemical Sensor 16 Assembly of CNTs CNT applications: Ultra-hard Composites Nanopipettes Field Emission Transistor Nanomanipulator Carbon Nanotubes Difficult to obtain in pure form (SWNT, MWNT, Cx, soot etc.) As-synthesized CNTs are a mixture of conducting, semiconducting and insulating ones Not stable under oxidizing conditions Little manufacturing control over tube diameter Nanowires Good transport properties - Single crystalline nature Mechanically robust - Defect free Flexibility in composition Doping possible to create p- and n-type nanowires Nanowires-based FETs and basic logic circuits demonstratedin the laboratory. Techniques for mass manufacture 19 Transport in Nanowires Conductance Quantization: The Landauer equation G = (2e2/h)N, N = no. of conduction channels When NW diameter is smaller than the Fermi wavelength, conductance changes in steps of 2e2/h 20 21 Synthetic Routes to Nanowires Epitaxial growth Catalytic VLS growth Catalytic base growth Defect nucleation Templated growth Arrested growth Assembly of nanoparticles 22 Epitaxial growth Active surface Masked surface Vapor-Liquid-Solid (VLS) Growth Start with a metal catalyst Form a liquid droplet of a metallic eutectic when heated Gaseous precursor feedstock is absorbed má HOC a 2 m 1r IW E *" a 1- / (■ / tj 3W ™1 |ÍM30*>S0«T9W« i» j^ Si content (atom%) gj The droplet becomes supersaturated Excess material is precipitated out to form solid NWs beneath the droplet 24 Vapor-Liquid-Solid (VLS) Growth Au Particles Alloy Liquid Nucleation of NWs NW Growth Vapor-Liquid-Solid (VLS) Growth Atoms Liquid Eutectic Substrate 100Q- p boo- eoo- F 400 WC 200f 0 Ali 20 40 60 eo 1C0 Weiflht%Gfl °* 26 Si Nanowire Growth Mass transport in the gas phase Chemical reaction at the V-L interface SiH4-> Si + 2H2 Diffusion in molten catalyst Incorporation of material in the crystal lattice Si Nanowires Defect-free Si NW Q JťiJclřiOO jskí^w OrOyíľvVvO^^^^^I "■:-1 3.BB nm» ?:&£:■-< ^^SBJSšJci ■:í'ľ. 28 In situ TEM images recorded during the VLS process 29 Size Control Metal particle acts as a soft template to control the diameter of the nanowire Au InP 10 nm o c Laser Ablation 20 nm Q ^^> dZ 30 nm Q C_ 30 Catalytic base growth Ge-Fe catalytic nucleus Ge wire Precursor supply Fe substrate 31 Templated growth 1. Pores filled with material by CVD Alumina 53—Pore 2. Alumina matrix dissolved W^ % % mí0lJI^-i 3. Wires separated I ä% if ^1^5^ »^ 1 "* ~% V5Ä Barr ier Alum i mum Film 200 nm 32 Arrested growth Precursor supply Growth direction Selective binding of a compound to certain crystal faces CdTe,TOPO blocks (111) Alivistos 33 34 Molecular rods A —a— || — II H-Hľ Ŕ ■ ~ô- ''"ô-" ^Ofr 1 H 1 |n . Z |1|I Infi * # ©•-£>- - i MM 4I 4 |IH lu|4 -g>- EL-IJ-H nfS^t -■#- -fl-H H^}]jtf 5 |l|i 1—■-= t |IK \*# -O- K>' ■ UP HP X |]|H hü H" n-f Vll I ř-jru^ IUP 1*1* -Q- -O ^ ■> um Mil W-. ML- ŕ ML, ■cQj-"-cQ>" h<3> i* MM* hl» •ir ' J-POtM 12 mih hi: I ľ H 11*4 . >H u mil; hU-> l+ I']'-1 HJ4 35 Fibers Viruses Bacteria Pollen Microfibers Hollow fibers Electrospun fibers | Carbon nanotubes Hair 0.901 0.01 0.1 1 Diameter [urn] 10 100 36 Electrospinning SEM MAG: 1.00 kx DET: BE Detector HV: 30.0 kV DATE: 0311 0108 VAC:HiVac Device: TS51 30 I__I__I__I__I___I__I__I__I__I__I 50 um Vega©Tescan . TU Liberec SEM MAG: 10.00 kl! DET: BE Detector HV: 30.0 kV DATE: 03/1 0Í08 VAC:HiVac Device: TS5130 5 um Vega©Tescan . TU Liberec 37 Electrospinning 10 kV bending and axisymetrical instability Rayleigh instability thickeness Adsorption of polymer molecules electric layer Left: Photograph of a jet of PEO solution during electrospinning. Right: High-speed photograph of jet instabilities. 39 Coaxial electrospinning 41 Multijet electrospinning Syringe pump system H VC D 1 PET plate Ngzzle Target ^electrode PET film 42