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UMD ENMA 490 - Carbon Nanotubes

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Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Carbon NanotubesDeanna ZhangChuan-Lan LinMay 12, 2003Overview•Introduction•History•Fabrication•Application•SummaryIntroduction I:What is nanotube?•Responsible bond:•Unit cell: honeycomb pattern•Wrapping these patterns back on top of themselves and joining the edges Carbon nanotube 2SPIntroduction II:Single and Multi-wall nanotube •Single wall nanotube: –SWNT–single atomic layer wall, diameter of 1-5 nm –excellent mechanical property– hot topic now •Multi wall nanotube:–MWNT–Inner diameter: 1.5 – 15 nm–Outer diameter: 2.5 – 30 nm– ~50 layers –containing more structure defects (http://www.lbl.gov)Introduction III:The Electrical Properties of nanotube•Can be either Metal or semiconductor–Controlled by Rolling DirectionCh (rolling vector)= na + mb (unit vector) Rule: = integer metallic non-integer semiconductor•Electrical Conductivity–Four Point Probe Method to determine sheet resistance and conductivity3mn Introduction IV:The Other Properties of Nanotube•Mechanical:–Young’s Modulus ~ 1TPa (SWNT), 1.25 TPa (MWNT) (Steel: 230 GPa)–Density ~ 1.3 g/cm^3•Thermal:–Conductivity: 2000W/m.K ( copper: 400W/m.K)•High Aspect Ratio: Length ~1µm, Diameter ~ 1nm to 50nmHistory IBuckyball ( )•The discovery of nanotubes comes from Buckyball•The discovery of Buckyball is by accident, from Radio-astronomy•Around 1970s60C(http://www.slb.com )History IIThe History of NanotubesWhen Who Events1970s Harry Kroto & Dave Walton Try to synthesize long carbon chainsLate 1980s Scientists around the world Buckyball was synthesized and confirmed as C601991 Japanese Scientist, Sumio Iijima Discovery of multi wall carbon nanotubes 1993S, Iijima and T, Ichihashi Synthesis of single wall carbon nanotubes1996 Robert F. Curl, Harry Kroto , Richard E. Smalley Nobel Prize in Chemistry for the discovery of Buckyball1999 Samsung Flat Panel display prototype2001 IBM The first computer circuit composed of only one single carbon nanotubeFabrication of Carbon Nanotubes•Laser Ablation or Pulsed Laser Vaporization•Carbon Arc or Arc Discharge•Chemical Vapor Deposition (CVD)•High pressure (HiPCO)Fabrication ILaser Ablation• Target: 1 at.% each of Ni and Co uniformly mixed with graphite• 500 m Torr Ar flowing at 50 sccm• In the oven at 1473 K• Nd:YAG Pulse laser at 60Hz• PUREST but yield is very small (~0.4 gram/hour)• Developed by NASA JSC Group based on Rice University facilityFabrication IICarbon Arc or Arc Discharge• The first available method• Electric arc vaporizes an carbon anode containing the catalysts (Ni and Co)• He: 500 Torr, Current: 100 amp and 35 volts• Chamber is cooled by water• Nanotube takes place at the wall inside the chamber• Developed by the group at the University of Monpellier, FranceFabrication IIIChemical Vapor Deposition (CVD)•Idea: prepattern the substrate with a catalyst and to grow nanotubes onto these by CVD •The key step : deposit the catalyst at predefined locations •Advantage: SELECTIVE GROWTH: we can grow nanotube at the place we expect •First developed by Xie group in China in 1996•Use hydrocarbons as sourceFabrication III:Steps of CVD •Deposit photoresist•Expose resist•Deposit catalyst•Etch resist•CVD growth of Carbon Nanotube on catalystFabrication IVHiPCO2CO• Single wall nanotube in gas phase (1200C, 10 atm)• CO+CO C+ catalyst: (25 mTorr)• Flow high pressure carbon monoxide past catalyst particles at high temperatures• Can now produce largely single-walled nanotubes in kilogram quantities • Purification steps are unnecessary due to use CO instead of hydrocarbons•(P. Nikolaev et al.)5FeCOApplication•Transistor–Field Effect transistor–Single electron transistor•SPM Tips•Field Emission Display Device•More Possible ApplicationsNanotube transistor•Field Effect transistor–Similar to MOSFET–Formation of P-type–Annealing or doping with K to form N-type–Use both N and P tomake CMOS typecircuitsSPM Tips•Tips of Scanning Probe Microscopes are usually cantilevers or metal wires but seldom survive a tip crash•Nanotubes: large aspect-ratio, well-defined end, far more resistantA nanotube was directly grown by CVD on a cantilever (From J. Hafner et al, Nature 398, 761 (1999))Field Emission Display Device•Take advantage of the properties of high current containing and high aspect ratio•Useful as the electron source for Flat Panel Display with lower power consuming and high voltage circuit is unneeded•Samsung has shown the prototype of 9” full color display with 576 X 242 pixels•The first nanotube flat screen TV is expected to be manufactured by the end of 2003 The Samsung 4.5” full-color nanotube display Schematic structure of nanotube flat panel display.(Choi et al.)(Cathode)(Anode)More Possible Applications•Nanotube sensors (Kong et al.):–The electrical conductivities of SWNT change dramatically when they expose to gaseous molecules•Hydrogen storage (Heben et al.):–5~10 wt% hydrogen storage density at room temperature for SWNT •Light Elements (Saito et al. ):–Electrons from nanotube bombard a phosphor-coated surface to produce light –2 times brighter, 8000h lifetime, can be used for giant outdoors displays•Memory device (Fuhrer et al.):Capable to store single electronic charge–High mobilitySummary and Future work•Carbon Nanotubes have unique properties•Unique properties lead to fabrication of different devices.•Improvements of current fabrication of carbon nanotubes needed to make available commercial products.•The totally new world constructed by nanotube is close.•Little knowledge about growth


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