1-Dimensional Nanostructures 1-Dimensional Nanostructures Aspect ratio (AR) = the ratio of length to diameter Cross section Internal twin structure Straight, wavy (worm-like), branched (dendritic) Solid or hollow Monocomponent, bicomponent, multicomponent Homogeneously mixed, spatially segregated Monocrystalline, twinned (1 or 5 twin planes), polycrystalline Nanorod (NR) (AR < 30) No widely accepted cutoff Nanowire (NW) (AR > 100) 1-Dimensional Nanostructures Core-Satellite Core-Sheath Hollow Branched (dendritic) Dimension-Properties Interplay Carbon allotropes Brilliant, Transparent Mohs Hardness 10 20 W/cmK High Melting point Metallic lusture, Opaque Black, Fibrous Black Shiny Crystals 1-2 1-1.2 25 6000 Lubricant Unusual Superconductor Electrical Behaviour (10-40 K) 4 Role of Dimensionality Dimensionality influences electronic structure From continuous bands to discrete energy levels Changes in electrical, optical, magnetic,....properties co 3D 2D ID Energy OD 3 D: 2D: 1 D: 2mL y J Im 2m K*+kr2+\*Ij- n 7ľ ^=1,2,3... =1,2,3. 1D Nanostructures JHC>w C-C-C-C-C-C DNA Molecular Wire The Nano World 250 um Poly (ethylene oxide) Collagen Fibrils Potential Applications of Nanowires Electron Transport 'Nano-cables' Core-shell Superlattice AFM & STM Tips Surface Modification Interconnects Novel probes Multifunctional Hierarchical alignment Building blocks for devices 7 Quantum Confinement Effect 1 1Ü 100 1000 10000 100000 Diameter (A) The band gap increases with decreasing diameter (quantum confinement) Mechanical Properties WS2 Graphite 9 Strain-stress curve of a nanotube Carbon Nanotubes • (Re)discovered by lijima (1991, NEC) • 1952 Russians (CO + Fe hot, SEM) • Rolled up sheet of graphene • Capped at the ends with half a fullerene Carbon Nanotubes Bulk graphite - molecular slabs (graphene) stacked together via weak van derWaals interactions The rim atoms of graphite (sp2) are only two-fold bonded - a dangling bond pointing outward, but the number of surface atoms is outnumbered by the three-fold-bonded "bulk" atoms The relative chemical energy stored by the rim atoms is negligibly small Flat graphite nanoclusters cannot tolerate the large chemical energy stored in the dangling bonds of the rim atoms of a small graphene sheet: - rolling to nanotubes - curling to fullerenes 11 Carbon Nanotubes Single Walled Nanotubes (SWNT) • Single atomic layer wall • Diameter of 0.7 - 5 nm • Length several microns to centimeters Double Walled Nanotubes (DWNT) • exactly two concentric CNT • the outer wall selectively functionalized while maintaining intact inner-tube Multi Walled Nanotubes (MWNT) • Concentric tubes ca. 50 in number, separation 0.34 nm • Inner diameters : 1.5 - 15 nm • Outer diameters : 2.5 - 150 nm Lengths: micrometers to centimeters Aspect Ratio: up to 107 SWCNT Diameter from Raman Spectroscopy • RBM (Radial Breathing Mode): 100 to 300 cm"1, vibration at which the nanotube diameter contracts and expands • D-band: vicinity of 1350 cm-1, defect-derived peak • G-band: vicinity of 1550 -1605 cm-1, in-plane vibration of graphite • G'-band: 2700 cm-1, overtone of D-band n •o Instrument: Hole >Lab Serie s 5000 ........7 I t 18 .................i?™* 4 on r1 J i 00 ■Ľ' k"' ...X- R B M 1-1343 J I r--V___j 0 250 500 750 1000 1250 1500 1750 2000 1 (532nm, x50,10sec) 1/cm The wavenumber of RBM is inversely proportional to the tube diameter D D (nm) = 248/U) = 248/184 = 1.3 (nm) 13 Raman Spectroscopy Virtual states Vibrational Infrared Raylelgh Stokes Anti-Stokes absorption scattering Raman Raman scattering scattering Raman scattering is an extremely weak process - only one in every 106 - 108 photons scatters Height ofthe peak -* Substance concentration <-i->■ Shift of the peak position -* stress Width ofthe peak —* crystallinity of material J_I_I_l_ t The position öf the peak -* molecular structure c Raman effect - interaction between the electron cloud of a molecule and the external electrical field of the monochromatic light - a change in polarizability with respect to the vibrational coordinate Anti-Stokes Raman scattered I ght Rayleigh scattered light Stokes Rarnan scattered light Stokesi lines; stronger than Anti-Stokes ! Wavenumber {cm"1) Wavelength (nm) -1000 505 -800 510 -600 516 -400 521 -200 526 0 532 200 538 400 544 600 550 800 556 1000 562 CNTs: Properties and Potential Electronic: Bandgap Eg~ 1/d Ballistic conductivity in metallic CNTs, the highest current density 109 A/cm2 (Cu only 106 A/cm2) SWNT - metallic or semiconducting, MWCNT - metallic Magnetic: Anisotropic magn. susceptibility X-L>> Xll Mechanical: Young's Modulus 1.8 -4.5 TPa (SWNT, axial), 0.95 TPa (MWNT) (Steel: 230 GPa) tensile strength above 100 GPa (steel: 1-2 GPa) the highest known Thermal: Conductivity theor. 6600 W/m K axial, 1.5 perpendicular, 3500 experim. (Diamond 3000, Cu 400 W/m K) 300 W/m K bulk SWCNTs, 3000 W/m K individual MWCNTs Thermal stability 650 °C (SW)-800 °C (MW) in air, 2800 °C in Ar (anealing to graphitize defects), 320 °C with metal oxides on the surface - O vacancies, Mars-van Krevelen catatlytic mechanism Synthetic Routes to CNT • DC arc discharge: growth on a cathode C electrode at 3000 °C, MWCNTs and SWCNTs (with catalyst), easy design, few structural defects, short tubes, low yield, low purity, random diameters • Laser ablation: primarily SWCNTs, few defects, good control over diameter, most costly method, poor scalability, requires Class 4 lasers, Co and Ni catalyst • Molten salt: primarily MWCNTs, simple process, used for filling CNTs, low yield and crystallinity, poor controllability • Chemical vapor deposition: both types, high yields, easy scalability, long tubes, alignment and pattern growth, some defects, medium purity 16 Synthetic Routes to CNT DC Arc discharge NTs observed in carbon soot of graphite electrodes during arc discharge (during production of fullerenes) The most used method of synthesis in early 1990's 2 carbon electrodes touch, T rises, gap, electric arch, fast e~ from cathode ionize He gas He+ attracted to cathode (-) Carbon (with catalyst) contained in negative electrode sublimes thanks to high temperatures of the electric discharge (3000 °C) Yield up to 30 %wt, produces both SWNTs, MWNTs Length up to 50 |jm, few structural defects Cathode — Inert Gas -Deposition -Anode - Synthetic Routes to CNT Laser ablation Pulsed laser vaporizes graphite target in a high-temperature reactor filled with inert gas (650 mbar, Ar, N2) CNTs develop on the cooler surfaces of reactor as the carbon condenses Pure graphite - MWNTs Graphite + metal catalyst particles (Co + Ni) - SWNTs Yield up to 70 %wt, few defects Controllable diameter of SWNTs by changing p, T More expensive than arc discharge, CVD Synthetic Routes to CNT Molten salt LiCI, LiBr, 600 °C, graphite electrodes Cathode exfoliates and graphite sheet wraps MWCNTs Yield up to 30 %wt, low purity Large number of defects, amorphous carbon impurity, salt encapsulating a II 19 Synthetic Routes to CNT CVD (Chemical Vapor Deposition) Substrate + metal catalyst particles (cobalt, nickel, iron) Distribution of metal catalyst and the size of the particles influence the diameter of NTs Patterned (or masked) deposition of metal, annealing, plasma etching Substrate is heated Two gasses are bled into the reactor - process gas (ammonia, nitrogen, hydrogen) and carbon-containing gas (acetylene, methane, ethylene) Carbon-containing gas is broken apart at the surface of the metal catalyst particle, carbon is transported to the edges of the particle, where it forms the NT Catalyst is removed by acid treatment Resulting NTs are randomly oriented 20 Synthetic Routes to CNT CVD (Chemical Vapor Deposition) CH4 + metal catalyst particles (cobalt, nickel, iron) Fe3C/C + H2 Tip growth Base growth FIGURE 9: Carbon nanotube mechanistic mc-d-els: (a] rMt-growth machartism e (bj tip-^rov/th mechi nisin. la) /CatalystN Catalyst Support Substrate (b) Catalyst- Catalyst Support Substrate i ( ^atalys 1 1 V Catal yst Support Substraie Catalyst Support Substraie Gmwih Nitipx Catalyst Support Substrate (PS f Catalyst^ CM I. Catalyst Support Substrate 21 Synthetic Routes to CNT CVD (Chemical Vapor Deposition) Plasma Enhanced CVD Plasma is generated by the application of strong electric field during growth Growing NTs follow the direction of the electric field With the correct use of reactor geometry, vertically aligned (perpendicular to substrate) NTs can be grown Substrate patterned (lithography) with Fe NPs CDV shows the best promise for industrial manufacturing of CNTs Better price/unit ratio NTs grown on desired substrates Synthetic Routes to CNT Super-growth CVD New methods of CVD using different substrates, catalysts Activity and lifetime of catalyst can be enhanced by adding water into the reactor Growing CNTs then form ,/forests" up to several mm high, aligned normaly Improved efficiency, reaction time and purity of CNTs (more than 99,9%) Hata, K.; Futaba, DN; Mizuno, K; Namai, T; Yumura, M; lijima, S (2004). "Water-Assisted Highly Efficient Synthesis of Impurity-Free Single-Walled Carbon Nanotubes". Science 306 (5700): 1362-1365. doi: 10.1126/science. 1104962. PMID 15550668 |lMiftX.;.;>M.| ■ -I u Synthetic Routes to CNT ■*-1~ *-v 1-2n,-n 2-25 nm Defect-free (11,111) SWNTs with Open Ends A bundle of (10,10) nanotubes held together with strong TT-TT-stacking interactions 25 Roll-up of (n,m) SWNTs Chiral vector (n,m) ,* ,4 .4 ,4 .9 ,* ,* « J J J J J J J V V V V V V V .JJJJJJJJ ***************** armchair 4* ^ 4f 4 ********* (n,n) armchair (n,0) zigzag (n,m) chiral TEM of a chiral CNT Roll-up of (n,m) SWNTs Roll-up of (n,m) SWNTs armchair zigzag chiral A) Armchair - an achiral metallic conducting (10,10) tube B) Chiral - semiconducting (12,7) tube C) Zigzag - an achiral conducting (15,0) tube All the (n,n) armchair tubes are metallic Chiral or zigzag tubes are metallic only if (n - m)/3 is a whole number, otherwise, they are semiconductors Roll-up of (n,m) SWNTs A 2D graphite layer the lattice vectors a1 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 1D unit cell. The rectangle represents an unrolled unit cell, defined by T and Ch (n,m) = (4,2) 29 Roll-up of (n,m) SWNTs Roll-up of (n,m) SWNTs Ch = nax + ma2 = (n, m) ( and 0 < m < n ) Tube diameter C II a o Y 2 + nm + m a. a. — aQ = 0.249 nm # = tan 1 yÍ3m/[m + 2n) e = o-30° a= 1.42 V3 = 2.49Á d(Csp2-Csp2) = 1.42 Á 32 Defects in SWNTs Atomic vacancies - reduction of tensile strength, electrical and thermal conductivity Topological (Stone Wales) defect - rearrangement of bonds into pentagonic and heptagonic pair (connected, no other types of rings known) Defects lead to phonon scattering - increased phonon relaxation rate - reduction of mean free path (reduction of ballistic conductivity) leads to reduced thermal conductivity 33 (d) (e) Defects in SWNTs Separation of CNTs Semiconducting CNTs - Separation by surfactants, (octadecylamine), a strong affinity Metallic CNTs - Separation by diazonium reagents, biomolecules, DNA -AC dielectrophoresis - 10 MHz, induced dipole, causes the two types of CNTs to migrate along the electric field gradient in opposite directions 35 Doping of CNTs Intercalation CNTs - Between walls of MWCNT - during synthesis or posttreatment On-wall substitution CNTs - N or B substitute for C - In-situ - element-containing precursor - Ex-situ - removal of C atom - graphite (n) or pyridine (n or p) type of group 36 Functionalization Possibilities for SWNTs A) defect-group functionalization B) covalent sidewall functionalization C) noncovalent exohedral functionalization with surfactants-wrapping D) noncovalent exohedral functionalization with polymers E) Endohedral functionalization with C60 (C60@CNT, "peapods) 37 Functionalization Possibilities for SWNTs 4000 3500 3000 2500 2000 1500 1000 50( Wawenumbers (cm1) 20nm Functionalization Possibilities for CNTs Reactions will occur first at the end caps, then on the surface, at structural defects Functionalization Possibilities for CNTs Ti02 and Si02 on acid-treated CNTs via ALD SEM image for the case of Si02 TEM image of vertically grown CNT coated with Ru02 both outside and inside 1 HO^O Hd *°H Step 1 OH =\ .O (M=Ti,Si) ci,m"o cyA Step 1 ^ Hydrolysis . o (HOJjM 'O (HOfcHl Assembly of CNTs CNT applications: Ultra-hard Composites Nanopipettes Field Emission Transistor Nanomanipulator CNT Applications CNT Applications CNTs as photosensitizers: (a) electron injection into the conduction band of Ti02 (b) electron back-transfer to CNTs with the formation of a hole in the valence band of Ti02 and reduction of the hole by oxidation of adsorbed OH" species 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 demonstrated in the laboratory Techniques for mass manufacture 44 Synthetic Routes to Nanowires Epitaxial growth Catalytic VLS growth Catalytic base growth Colloidal synthesis Defect nucleation Templated growth Arrested growth Assembly of nanoparticles 45 Epitaxial Growth Active surface Masked surface Vapor-Liquid-Solid (VLS) Growth (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 20 40 60 80 100 Weight percent Si (Ge) Eutectic 360 °C Au (mp 1064 °C) Si (mp 1410 °C) Ge (mp 938 °C) 47 1 Vapor-Liquid-Solid (VLS) Growth 1200^ 1000-1 u o lllllllll|MIIIIIII|lllllllll|lllllllll|lllllllll|lllllllll|IIMIIIII|lllllllll|lllllllll|IIIIIIIUJ 1064 °C 938 °tí 400-3 L+Ge V (29%,320°C) 200^ III IMIII|MIIMIII|IIIIMIII| III EMI lij III MIMI| III IMMI| III III lll| IIIIII Ml| Ml MM II|III1IIIM 0 20 40 60 80 100 Au Ge atomic % Ge 48 Vapor-Liquid-Solid (VLS) Growth Nucleation of NWs M(Ge)/% In-situ TEM images of the VLS process ln-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 50 Ge NWs on the Bare Ge(110) Substrate Precursor Elements (vapor) a metal catalyst substrate A f Heat . J '. . ✓* i w .4 ir Supers aturation d ) /uH : CD 1D structure Si Nanowire Growth SiH4^ Si + 2H2 Mass transport in the gas phase Chemical reaction at the V-L interface Diffusion in molten catalyst ft ^ Incorporation of material in the crystal lattice 6 52 Si Nanowires Size Control Metal particle acts as a soft template to control the diameter of the nanowire 54 Catalytic Base Growth Ge-Fe catalytic nucleus Ge wire Precursor supply Fe substrate 55 Colloidal Synthesis Anisotropic shape 1D instability LaMer mechanism (A)f u c o U u £ o ■4-« < u max critical limiting supersaturation cnu min cs / solubility _ / °o°00 / O O 0 / o a / o e / generation / of atoms self-nucleation growth Time The concentration of atoms increases with time as the precursor is decomposed The concentration reaches the minimum level of supersaturation, Cmin, the atoms start to aggregate to generate nuclei and then seeds - homogeneous nucleation The seeds grow in an accelerated manner because of autocatalysis, the concentration of metal atoms in the solution drops quickly The concentration drops below the minimum level of supersaturation, no more nucleation A continuous supply of atoms - decomposition of the remaining precursor, the seeds will grow into nanostructures with increasing sizes until the synthesis is terminated or an equilibrium state is reached between the atoms on the surface of the nanostructures and free atoms in the reaction solution Colloidal Synthesis Seeding - heterogeneous nucleation - a much smaller driving force a lower concentration of atoms or a lower reaction temperature) is needed Homogeneous nucleation a f ŕ Heterog IF / ynp nuclead eneous on (C) \G (A) solution reduction (B) surface reduction red ox e homogeneous nucleation adsorption heterogeneous nucleation metal precursor ion Q metal atom I mř e* UJLLUJUoB BdUUULUJd 57 Assembly of Nanoparticles (A) random aggregation (B) orientated attachment (C) hard template (D) soft template i hi 58 Tern plated Growth 1. Pores filled with material by CVD Arrested Growth Precursor supply Growth direction Selective binding of a compound to certain crystal faces CdTe, TOPO blocks (111) Alivistos 60 SLS-growth Mechanism Nanoengine 20 Mm Nanoengine runs on catalytic reactions: Pt part splits H202 to 02 and protons H+. Excess electrons move to Ag/Au, reduce H202 and protons to water. Release of 02 causes streaming that propels the engine through the liquid 150 micrometers per second Joseph Wang UC San Diego and Arizona State 62 Inorganic NanoTubes INT - MoS2, WS2 B Furnace • ••••••• Quartz tube Hg/Ng + H2S- bbs:—*Mo03-. +^ Substrate Gas-Phase reaction nested fülle rene-like sublimation of M0O3 powder with 5 pm particle size B M0S2 Solid-Phase reaction mos2 M0S2 nested fullerene-like WO3 <200 run WS2 WS2 WS2 Inorganic NanoTubes INT Defect free INT-WS2; (a) SEM image (b) TEM image (scale bar 10 nm) 64 ZnO Nanorods Molecular Rods i] [if* l,2ff-BuLi 2.O1CI2 3. HiO+ |4|6 \216 Hit Ml' -<\>- '^@-n H©+H HH2^H H-fet" 11 kll 4 MM lull ■■ —KS-H Ii- stat-ii s 111 -= hi* ■o- ■*<>» 4$? -g- ,c-g-H 7 llT |M|7 » in» I" if t |]|H lit* II I. it- BtiLi H_ * 2.R3SiCl H SiR, BuL: I 1. ir-BüL \l, C«C12 >-SiR3 'OK i>: Re- : in' ON ON Rt^-==- I n-BuLi 2. Cul I.Br-=-SiMcj,EtNH: 2-MeOHtK,C03 Lfl-BuLi :. 1 hi OK Rc-= : — Ol Br — = SiMej RtNH: Kc- I MeOH, KOH 2, CwfOAc)^ pyridine 66^ on' Re. Cp* Fibers Viruses Bacteria Pollen Hollow fibers M icrofibers Electrospun fibers | Carbon nanotubes Hair 0.001 0.01 0.1 1 Diameter [urn] 10 100 67 Electrospinning SEM MAG: 1.00 kx DET: BE Detector HV: 30 0kV DATE: 03110Í08 VAC: HiVac Device: TS5130 whipping - , vega©Tescan TU Liberec stabil jet Taylor cone SEM MAG 10 001« DÉT: BE Detector □ATE: 03/1 0/OS Device: TSS130 10 kV i collector bending and axisymetrical instability Rayleigh instability thickeness Adsorption of polymer molecules electric layer Electrospinning Electrospraying Electrospinning Parameters: • Solution (viscosity, conductivity, surface tension) • Instruments (voltage, distance b/w electrodes, collector shape) • Ambient (temperature, humidity, atmosphere) 69 Electrospinning ■Pi p Left: Photograph of a jet of PEO solution during electrospinning Right: High-speed photograph of jet instabilities 70 Taylor Cone Mg m f Volume Charge Density Needle-Collector Distance PA fibers, electrode distance 2 cm (a) and 0.5 cm Conductivity Morphology of fibers as a function of electric current (a) 20 hm.% PU (b) 20 hm.% PU with addition of 1.27% TEAB 76 Relative Humidity i—■—i—1—i—1—i—■—i—*—i—'—r- 0 10 20 30 40 50 60 Relative Humidity (%} PEO fiber diameter as a function of relative humidity 77 Coaxial Electrospinning Side-by-Side Electrospinning Solution A Solution B H / / 79 Multijet Electrospinning Needle-less Spinning Inorganic Fibers Th(acac)4; PVP; EtOH; acetone Electrospinnin Th02 82 Soft-Tern plating Ar Quart/ tube Furnace ■ J g\ t: t. c (. t, ti ti r r r> r t t —=fl^=y Quart? boal Thermocouple Ml C I' «' C, CDOC Vacuum pumping system Na2W04 + CTAB - hydrothermal = lamellar mesostructured composite [CetylMe3N]+ W042" Pyrolysis and carbothermal reduction in vacuo at 500 - 850 °C W nanowires - single crystallites grew along the [110] direction Also Cd, Cu and Co 83 Hard-Templating Impregnation of PTA (IIjPWhO^IIjO) SB A-15 Solvent evaporation-induced impregnation I " I |_ 800 j Removal tif the SBA-15 template Metallic W Nanowire bundles V SBA-15 1 200 1 1 Phosphotungstic acid (H3PW12O40.6H2O, PTA) precursor is completely filled into the mesochannels of SBA-15 via a solvent evaporation-induced impregnation H2 as a reducing agent at a temperature of 800 °C for 3 h Etching the SBA-15 template with HF 5% aqueous 84 Hard-Templating Tobacco mosaic virus (TMV) the first virus discovered Amine groups in the Inner diameter 4 nm channel complex with Pd(ll) Length 300 nm or pt(||) The outer surface no amine groups The selectivity for binding of metal ions to the interior of the TMV After activation of the channel with Pt(ll) or Pt(ll), Ni deposited within the TMV channel in an electroless plating bath: Ni(ll) + (CH3)2NHBH3 Chemical Vapor Transport The chemical vapor transport of tungsten in the presence of oxygen onto substrates kept at temperatures higher than the tungsten oxide decomposition temperature (1450 °C) Substrates were placed close to the filaments (0.5 mm diam) at a distance of 1 mm or less 02 flow rate was varied from 0.03 to 0.1 seem in 90 seem of either N2 or Ar Experiments were performed at different filament temperatures ranging from 1200 to 2000 °C and at a pressure of 150 mTorr nano wires) Chemical Vapor Transport W + 02 -> W02 (g) AG = -40.08 kJ/mol K (1450 °C) W02 (g) -> W (s) + 02 AG = -267.33 kJ/mol K (1500 °C) Electrical Feed-throughs * .. % >\ Vis Filament ^Substrate (W nanowires) Second Substrate (WO, nanotubes and nanowires) N2/Ar O Chemical Vapor Deposition W03 + H20 -> W02(OH)2 W02(OH)2 + 3H2 -> W + 4H20 Directional Solidification of a Eutectic Alloy Arrays of single crystalline wires embedded in a single crystalline matrix Ni-AI -W 1.5at.%W Directional solidification in a Bridgman type crystal growing facility The crucible support, cooling ring and heating element (tungsten net) The alumina crucible -1700 °C for initial melting thermal gradient 40 K cm-1 a growth rate of 30 mm h~1 inter-phase spacing 89 Directional Solidification of a Eutectic Alloy |-NiAlW alloy Digestion of the matrix HCI (32%):H202 (30%):H2O, 10:10:80 the potential oscillates between 0.150 and -0.025 V SHE reference electrode Electrochemical oxidation Directional Solidification .W NiAl Etching Domo um The counter electrode - a strip of Pt foil pH of 6.0 Complete wire removal Further etching Nano-sized filler 90 Directional Solidification of a Eutectic Alloy The tungsten wires A diameter of 200 nm and the mean inter fibre spacing 3 um The fibre orientation was 100 referring to the rod axis High aspect-ratios (>1000!) 91 Directional Solidification of a Eutectic Alloy lug (17ms"1) The growth rate V and the nanowire spacing A The increase in the growth rate results in the decrease of wire diameter and an increase in wire density A2V = const The growth rate increases, the effect of the lateral diffusion flux along the solid/liquid interface diminishes and the boundary layer thickness increases These changes in the growth conditions at the solid/liquid interface lead to a decrease in the fibre spacing ^ Directional Solidification of a Eutectic Alloy •6 25 -6 30- _ -6.35-E 2- -6 40-J? -6 45- -6 50 -6 55- -64 —I— -60 —I— -5 6 -1— -5? —I— -48 —I— -4 0 log (I /im ) -5 45 -5 50 -5 55 -560 -5 65 -5 70 - -5 75 -5 80 -3 6 The nanowire diameter, a, is related to the spacing, A, and the volume fraction of the wires, Vf: a2 = gVf A2 g = the geometrical factor dependent on the fibre arrangement -B- 1 10 urn aj — IB Mill polymer nanoscmor ^ embedding array tip sharpening j, field emitter surface fnticflonallsation Mill 11111 wettability itudiei mechanical testing 93 Cold-Field Electron Emission Keith ley 237 HV SMU Micromanipulator - Anode tip Substrate or etched tungsten tip (cathode) Tungsten Core The ions are formed by direct electron impact from the field-emitted electrons M(CO)n + e"^M(CO)n_x+ + x CO + 2e~ 8.47 eV W(CO)6, Fe(CO)5, Co2(CO)8, Co(CO)3NO, benzene, naphthalene, acetylene, Tetramethyl silane 1D Metal Nanostructures Electronic, plasmonic, magnetic, electrical, mechanical, and thermal properties Optical transparency Electrical conductivity Mechanical flexibility Magnetic anisotropy (Fe, Co, Ni) • Touchscreens • Flexible solar cells • Optical sensors • Contrast agents for biomedical imaging • Therapeutic agents for cancer treatment • Electrocatalysts • Electrically and thermally conductive composites • Wearable electronics 95 1D Metal Nanostructures Monometallic Multimetallic Heterogeneously structured systems (A) Alloyed (B) Segmented (C) Tadpole-like (D) Dumbbell-like (E) Core-shell (F) Core-satellite (G) Multiwalled nanotube (A) (B) (C) (D) (E) (G) 96 1D Metal Nanostructures Localized Surface Plasmon Resonance Anisotropic shape Two LSPR modes - transverse and longitudinal directions "90 nm {< 10 nm 50 nm Increasing aspect ratio 400 600 800 1000 Wavelength (nm) 1200 12 10 o ~ 8 flj a* 6 Q. co < 4 600 700 800 900 1000 1100 1200 1300 Wavelength (nm) 97