Presentation on theme: "The exciting future of fullerenes"— Presentation transcript:
1The exciting future of fullerenes Carbon Nanotubes:The exciting future of fullerenesPapers used:“Carbon Nanotubes: Present and Future Commercial Applications ““Single-Wall Carbon Nanotubes”“Carbon nanotube mass production: principles and processes”“Fabrication and multifunctional properties of a hybrid laminate with aligned carbon nanotubes grown in situ”Presented By:David ChaarSteven HeringPhillip ThaneKori Mondin
2ABSTRACTCurrently CNT’s are used in specialty applications such as bikes, boats, and race cars because of CNT’s very light weight compared to competing high strength materials. Most recently CNT’s have been used in batteries, transistors, and even as a shield against space debris for NASA’s Juno spacecraft.The increasing demand for CNT’s is driving advances in CNT synthesis, purification, and chemical modification technology. The advances in production are beginning to create new applications for CNT’s that go beyond the incorporation of bulk powders. The most promising areas of research are microelectronics, biotechnology, water purification, and composite materials.
3Less than 100nm up to several cm IntroductionCarbon nanotubeslayers of carbon bonded in hexagonal latticesform large sheets of graphenewhen sheets are rolled up they form tubes which are existent at a nanometer scaleSingle Walled CNTMulti Walled CNTLengthLess than 100nm up to several cmDiameter.8-2nm5-20nmL/D100- 4x10^720-2x10^6Thermal Conductivity3500 W/mK(>diamond)-Tensile Strength100 GpaTwo types of CNTsmulti walledmake incredibly strong fiberssingle walledwell suited for electrical and thermal conductionthe strength of a MWNT is ten times higher than any other known fiber!
4Electron Structure of Nanotubes Properties stem from “graphene”Conducting properties determined by nature of electronic states near Fermi energyenergy of highest occupied electronic state at zero temperatureBand structureUnlike metal or semiconductorIn betweenMost directions, electrons at Fermi energy are backscattered by atoms in the latticeOther directions, electrons that scatter from different atoms in lattice interfere destructively and suppresses backscatteringOnly happens in y direction and directions 60°, 120°, 180°, 240° from y
5Electron Structure of Nanotubes Converting 2-D to 1-D forms tubeResulting boundary conditions on wavefunction quantizes kn, component of k perpendicular to axis of tubekn =2πn/CTube axis in y direction: tube acts as 1-D metalTube axis in different direction: semiconducting 1-D band structureConverting from 2D to 1Dsimply a matter of changing the tube orientationusually done with an electrical currentIf CNT is turned such that the axis is pointing in the metallic direction it results in a tube whose dispersion is a slice through the center of a cone. The reason it's called 1D at that point is because the fermi velocity is comparable to typical metals.
6Nanotubes: how they conduct Attach metal electrodesCan be connected to single tube or bundle of several hundred tubesDrop tubes onto electrodes (a)Deposit tubes on substrate, locate with scanning electron microscope, attach leads to tubes using lithography (b)Advanced techniquesGrowing tubes between electrodesAttaching tubes to surface in controllable fashion using electrostatic or chemical forcesSource and drain allow conducting properties to be measuredab
7Nanotubes: how they conduct Gate used to electrostatically induce carriers into tubeNegative bias on gate induces positive charges on tubePositive bias induces negative chargesConductance of tube measured as function of gate voltage
8CNT Synthesis Chemical vapor deposition Chemical vapor depositionMost commonly used method of high volume CNT productionA catalyst is placed in a reactor and carbon containing gas is pumped through at a specific temperature and pressure so that it forms graphene on the surface of the catalystCurrent bulk production methodsleave a large number of impurities and contaminantsmust be washed out with chemical treatmentscan reduce CNT length and cause defects in CNT sidewalls
9Post Production Processing: Chemical vapor deposition creates a bulk powder of CNT’s. Currently research is being done to find how catalyst and production conditions influence CNT chirality, diameter, length, and purity.Post Production Processing:High purity SWNT powders are created by separating bulk powder by density or gel chromatography. Following this various washes and thermal treatments are used to create stability on the CNT surface by addition of surfactants.Bulk CNT PowderSeparation of three proteins by gel chromatography. In the same way, CNT’s can be separated based on density.
10CNT Production: Bottom-line Laser AlignmentUsing lasers, single walled carbon nanotubes can be synthesized with large lengths, if this process can be scaled up then the cost of processing and purifying bulk powders to achieve desirable lengths could be avoided.Self Aligning GrowthSynthesis of long CNT’s could be done without expensive and time consuming liquid processing by coating substrates with catalyst particles which cause the CNT’s to line up together as they grow.
11Composite Materials Electrically conductive fillers in plastics CNT powders mixed with polymersIncrease stiffness, strength, toughnessNo compromise in mechanical propertiesCNT resinsEnhance fiber compositesWind turbines, boat hulls
12Composite MaterialsMWNT added as flame retardant additives to plasticsChange in rheology by nanotube loadingYarnHigh surface area increases strength when knotted
13Work performed – CNT synthesis (MWNT) Use of Fluidized bed reactors for CVDAllows for uniform gas diffusionAllows for heat transfer to metal catalyst nanoparticlesHas allowed for factors to greatly decrease MWNT commercial pricesScale-upUse of low cost feed stocksIncrease in yields
14Work performed – CNT synthesis (SWNT) SWNT synthesis by CVD requiresSeparation according to chirality by density gradient centrifugation + surfactant wrapping or gel chromatographyStable CNT suspensions will require addition of surfactantWashing or thermal treatment needed to remove surfactantVery tight process controlSWNT >> MWNT
15Work performed – CNT synthesis Synthesis of long, aligned CNTsPreferably without requiring to disperse in a liquidMethods includeSelf-aligned growth of horizontal & vertical CNTS on substratesSubstrates are coated with catalyst particles
16Work performed – CNT synthesis Can synthesize CNT forests and manipulate intoThin filmsIntricate 3D microarchitecturesDirectly spun into long yarnsDrawn into sheets
17Work performed – Composite Materials To organize CNTs at a large scale, fiber composites are created by growing aligned CNT forests onGlassSiCAluminaCarbon FibersCreates fuzzy fibersImproves toughness by more than 50%
18Work performed – Coating and Films CNT can be a multifunctional coating materialLeveraging CNT dispersionFunctionalizationLarge-area deposition techniquesExample:MWNT containing paints reduce bio-fouling on hullsAnticorrosion coating on metals while providing stiffness and strength
19Work performed – Coating and Films CNT-based transparent conducting filmsAlternative to expensive indium tin oxide (ITO)Flexible, and not brittleApplication inDisplaysTouch screen devicesphotovolatics
20Work performed – Coating and Films CNT conductors can be deposited from solutionSlot-die coatingUltrasonic sprayingCan be patterned by economic nonlithographic methodsRecent developments have allowed forSWNT films with 90% transparencySheet resistivity of 100 ohm per squareAdequate applications such as CNT thin-film heaters like defrosting windows or sidewalks
21Work performed – Microelectronics SWNTs are attractive for transistors due toLow electron scatteringBand-gapDepends on diameterDepends on chiral angleAlso compatible with field-effect transistor (FET) architectures and high k-dielectrics.Current densities achieved were greater than those obtained for Si devices.
22Work performed – Microelectronics CNT arrays containing SWNTs in patterned films increasesOutput currentCompensates for defects and chirality differencesImproves device uniformity and reproducibilityUp to 105 CNTs on a single chip
23Work performed – Microelectronics CNT thin film transistors (TFT) appealing for organic light emitting diodes (OLED) displaysHigher mobility than amorphous SiCan be deposited at low T, and non-vacuum methods
24Work performed – Microelectronics CNTs can replace Cu in microelectronic interconnects.Low scatterHigh current carrying capacityResistance to electromigrationCNTs can be used in high-power amplifiers and function as bothElectric leadsHeat dissipaters
25Work performed – Energy Storage Use of MWNTs in Li-ion batteriesLaptop notebooksMobile phonesMWNT powder blended with active materialsIncreases electrical connectivityIncreases mechanical strengthEnhances cycle life and rate capability
26Work performed – Energy Storage (supercapacitors) Study on packaged cells utilizing forest-grown SWNTs revealed remarkable performance16 Wh kg-1 energy density10 kW kg-1 power density16 year lifetime forecastThe only drawback is the high cost of SWNTs
27Work performed – Energy Storage (Fuel Cells) Use of CNTs in fuel cells as catalystReduce Pt usage by 60%For organic solar cells, CNTsReduce undesired carrier recombinationEnhance resistance to photo-oxidation
28Work performed – Environment (Water filters) Application of tangled CNT sheets to provide robust networks that have controlled nanoscale porosity and are robustMechanicallyElectrochemicallyUsed to electrochemically oxidize organic contaminants, viruses, and bacteriaEnhanced permeability will enable lower energy cost for water desalination
29Work performed – Biotechnology CNTs have been investigated as components ofBiosensorsMedical devicesAppeal due to compatibility with biomolecules (DNA/proteins) from two aspects:Dimensionalchemical
30Work performed – Biotechnology CNTs enable biological functions likeFluoroscencePhotoacoustic imagingLocalized heating via near-infrared radiation
31Work performed – Biotechnology (SWNT biosensors) Adsorption of target molecules on CNT surface allow for large changes inElectrical impedanceOptical propertiesApplication includeGas and toxin detection in industry and militaryTest strips for hormones and biological markers (NO2,troponin, estrogen, progesterone)
32Work performed – Biotechnology (In vivo) CNT can be loaded with cargo on walls or inside tubeAttaches to cell membraneRelease cargo upon near-infrared radiation
33Nanotube transistors Semiconducting nanotubes Tube turned on: negative bias to gateInduces holes on tubeMakes conductiveTube turned off: positive bias to gateDepletes holesDecreases conductanceResistance of off state can be more than million times greater than on statesimilar to p-type metal-oxide-silicon field effect transistor
34Nanotube transistorsConductance limited by barriers that holes see as they traverse tubeBarriers caused bystructural defects in tubeAtoms absorbed on tubeLocalized charges near tubeHoles see peaks and valleys that they must hop through if tube is to conductResistance dominated by highest barriers
35Nanotubes as one-dimensional metals Have large number of carriersConductance much larger than semiconducting nanotubesConductance oscillates as function of gate voltageOscillations occur when additional electron is added to nanotubeRegular and periodic oscillations: electronic states extended along entire length of tubeElectrons can travel long distances in nanotubes without being backscattered
36Nanotubes as one-dimensional metals 1-D conductor at low voltage makes it ideal system to test ideas about electrons1-D repulsive Coulomb interactions between neighboring electrons should behave differently than 2-D or 3-D2-D/3-D (a)Behaves as Fermi LiquidElectrons fill low energy states up to Fermi energyLow energy excitations act like free electrons (can tunnel without difficulty)1-D (b)Low energy excitations are collective excitations of entire electron system
37New Devices and Geometries Crossing metallic and semiconducting tubeMetallic tube locally depletes holes in semiconducting tubeElectron travelling tube must overcome barrierApplying voltage at one end of tube leads to correction at that end but not otherNanotube coilsIndividual tube loops back on itself to form ring-like structureUsed as solenoids to create magnetic fields or study quantum interference phenomena
38Future WorksInvestigate why yarns and sheets have thermal, electrical, and mechanical properties that are significantly lower than individual CNT.
39Future Works Better understand CVP process condition Reduce contaminantsAvoid costly thermal annealing and chemical treatments
40Future Works Better understand how CVP process conditions effect ChiralityDiameterLengthPurity
41Future Works Further price reductions of SWNT needed Commercial application of SWNT is emergingApplications require chiral-specific SWNTsSynthesize long aligned CNTs without the need to disperse in a liquid
42Future WorksImprove resistivity of transparent SWNT films so that they are better than equally transparent, optimally doped ITO coatings.
43Future Works Difficult control of CNT Diameter Chirality Density placementIntroduces difficulty to control microelectronic production over large areas.Required improved understanding of CNT surface chemistry for better commercialization of CNT TFT
44Future Works CNT biotoxicity Must control CNT retention within body Prevent undesirable accumulationBetter understand surface chemistry and geometryMedical application requires better understanding of interaction of CNT with the immune systemDevelop exposure standards forInhalationIngestionSkin contactInjection
45Conclusions Films Biotechnology Energy storage Coating MicroelectronicsWater filtersTransistorsBiosensorsscreensEnvironment
46ReferencesM.F.L De Volder, S.H. Tawfick, R.H. Baughman, A.J Hart, Carbon Nanotubes: Present and Future Commercial Applications. Science 339, 6119 (2013)P.L McEuen, Single-wall carbon nanotubes. Physics World 13, 6 (2000).Q. Zhang, J.-Q. Huang, M.-Q. Zhao, W.-Z. Qian, F. Wei, Carbon nanotube mass production: principles and processes. ChemSusChem 4, 864 (2011).E. J. Garcia, B. L. Wardle, A. J. Hart, N. Yamamoto, Fabrication and multifunctional properties of a hybrid laminate with aligned carbon nanotubes grown In Situ. Compos. Sci. Technol. 68, 2034 (2008).