• Share
  • Email
  • Embed
  • Like
  • Save
  • Private Content







Total Views
Views on SlideShare
Embed Views



0 Embeds 0

No embeds



Upload Details

Uploaded via as Microsoft Word

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
Post Comment
Edit your comment

    Reference Reference Document Transcript

    • 1. S. Iijima, Helical microtubules of graphitic carbon, Nature (London), 1991,354, 56-58.2. S. Iijima, and T. Ichihashi, Single-shell carbon nanotubes of 1-nm diameter,Nature (London), 1993, 363, 603-605. 1. 3.R.S. Ruoff et al. Carbon 33(7), 925 (1995). Iijima, S. Nature, 1991, 354, 56. 2. Meo, M.; Rossi, M. Composite Science and Technology, 2006, 66,1597. 3. Tans, S.J.; Devoret, H.; Thess, A.; Smalley, R.E.; Geerligs, L.J.; Dekker, C. Nature, 1997, 386, 474. 4. Arnold, M.S.; Green, A.A.; Hulvat, J.F.; Stupp, S.I.; Hersham, M.C. Nature Nanotechnology, 2006, 1, 60. 5. Tan, Y.; Resasco, D.E. J. Phys. Chem. B, 2005, 109, 14454. 6. Miyata, Y.; Yanagi, K.; Maniwa, Y.; Tanaka, T.; Kataura, H. J. Phys. Chem. C, 2008, 112, 15997. 7. Jorio, A.; Santos, A.P.; Ribeiro, H.B.; Fantini, C.; Souza, M.; Viera, P.M.; Furtado, C.A.; Jiang, J.; Balzano, L.; Resasco, D.E.; Pimenta, M.A. Phys. Rev. B, 2005, 72, 075207. 8. Bachilo, S.M.; Strano, M.S.; Kitrell, C.; Hauge, R.H.; Smalley, R.E.; Weisman, R.B. Science, 2002, 298, 2361. 9. Lolli, G.; Zhang, L.; Balzano, L.; Sakulchaicharoen, N.; Tan, Y.; Resasco, D.E. J. Phys. Chem. B, 2006, 110, 2108. 10. Itkis, M.E.; Perea, D.E.; Jung, R.; Niyogi, S.; Haddon, R.C. J. Amer. Chem. Soc., 2005, 127, 3439. 11. Nair, N.; Usrey, M.; Kim, W-J.; Braatz, R.D.; Strano, M.S. Anal. Chem., 2006, 78, 7589. 12. Rensselar Polytechnic Institute. Ajayan and Zhou. http://www.rpi.edu/locker/38/001238/pdfs/applications%20of %20nanotubes. pdf. (accessed Mar 03 2009).Jorio, A.; Dresselhaus, G.; Dresselhaus, M.S. (Eds.). Carbon Nanotubes, Topics inApplied Physics.,: Springer-Verlag, New York (2008)..Trademarks : SWeNT and CoMoCAT and registered trademarks ® ®of Southwest Nanotechnologies, Inc. HiPCo is a registered®trademark of Carbon Nanotechnologies, Inc. 13.ConclusionDespite early excitement about SWNT materials and theextraordinary amount of research inspired by their discovery, todate, commercial exploitation of the technology has beendisappointing. Perhaps there is insufficient understanding of thepractical hurdles to their commercialization. However, momentum
    • seems finally to be building, driven by substantial recent progressin these fundamental areas:Metrology and Quality Control: The concept of “if you can measureit, you can improve it” applies here. The means are now availableto adequately characterize SWNTs and to assure consistency ofthe materials needed for commercialization. Supporting this is thesoon to be available offerings by NIST of Standard ReferenceMaterials for calibration purposes.Improved selectivity: Driven by applications that require more thana near-random distribution of tube chiralities, there has been ademonstration of the means to substantially narrow the ‘asproduced’ chirality distributions of commercial scale productionproducts. There is also promising work toward achieving furtherselectivity through secondary processing.Dispersion: Recent years have seen the emergence of improvedaids to disperse SWNTs for formulation in inks and composites.Scale-up of manufacturing process: The last five years have seendevelopment and a maturing of scalable SWNT manufacturingprocesses, which can provide commercial quantities of SWNT withhigh purity, controlled properties and consistent qualitySWNT ApplicationsThe numerous unique properties of SWNTs have led to theirapplication in a wide range of technological problems. Their 12extraordinary mechanical strength is exploited in enhanced carbonfiber and reinforced resins and elastomers; their highly conductive 13nature and large surface areas are utilized to prepare conductivepolymer blends and films, improved lithium ion batteries, and supercapacitors. Unique optical properties allow for their use aselectrodes in displays, solarcells, and emerging solid state lighting
    • technologies. The semiconducting nature of some SWNT speciesallow their adaptation to logic devices, non-volatile memoryelements, sensors and security tags. It seems that new SWNTapplications emerge regularly, limited only by the creativity ofscientists and engineers working in the fielThe field emission characteristics of the body for single-walledcarbonnanotubes (SWNTs) are investigated by use of the first-principles calculations.We find that field emission property, chemical stability and binding energy of the tube body with the practical diameter are less sensitive to the tubediameter, morphology, and conductive characteristic, and conclude the emission features of the body film: consistence in emission sites, uniformity inemission energy distribution, predictability in emission effects and high emission stability, which are similar to those of graphite sheet or diamond film.These unique features guarantee the tube body to be applicable to flat panel displays with the same picture quality, cylindrical cathode and linearemitter.Structure of Carbon NanotubesSingle walled carbon nanotubes are an allotrope of sp hybridized 2carbon, similar to fullerenes. The structure can be thought of as acylindrical tube comprised of 6-membered carbon rings, as ingraphite. The cylindrical tubes may have one or both ends cappedwith a hemisphere of the buckyball or fullerene structure.An understanding of SWNT structure requires familiarity with theconcept of nanotube chirality, since the chirality of a SWNTdictates many of its properties. A concept known as a ChiralityMap, illustrated in Figure 1, has been developed as a tool forunderstanding chirality and its implications.A SWNT can be envisioned as a sheet of graphite one atom thickrolled into a tube (see inset in Figure 1). The chirality describesboth the orientation and diameter to which the sheet is rolled. EachSWNT on the chirality map is defined by two integers, (n,m). Asindicated previously chirality defines many of the properties of theindividual SWNT. For example, SWNT shown on the chirality mapin blue are metallic in nature. These are tubes where n=m
    • (armchair) or n - m = 3i, (where i is any integer.) Those depicted inyellow are semiconducting, displaying different band gapsdepending on the length of the chiral vector.Figure 1. A graphic displaying a Chirality Map which shows the various types of SWNTs that can be forfmed.The properties are governed by the wayin which they are rolled as shown in the insert. The SWNT will be metallic in the armchair configuration, or when m-n is a multiple of 3.
    • Cvd methodThe catalytic vapor phase deposition of carbon was reported in 1952[68] and 1959,[69] but it was not until 1993[70] that carbon nanotubes were formed bythis process. In 2007, researchers at the University of Cincinnati (UC) developed a process to grow aligned carbon nanotube arrays of 18 mm lengthon a FirstNano ET3000 carbon nanotube growth system.[71]During CVD, a substrate is prepared with a layer of metal catalyst particles, most commonly nickel, cobalt,[72] iron, or a combination. [73] The metalnanoparticles can also be produced by other ways, including reduction of oxides or oxides solid solutions. The diameters of the nanotubes that are tobe grown are related to the size of the metal particles. This can be controlled by patterned (or masked) deposition of the metal, annealing, or byplasma etching of a metal layer. The substrate is heated to approximately 700°C. To initiate the growth of nanotubes, two gases are bled into thereactor: a process gas (such as ammonia, nitrogen or hydrogen) and a carbon-containing gas (such as acetylene, ethylene, ethanol or methane).Nanotubes grow at the sites of the metal catalyst; the carbon-containing gas is broken apart at the surface of the catalyst particle, and the carbon istransported to the edges of the particle, where it forms the nanotubes. This mechanism is still being studied. The catalyst particles can stay at the tipsof the growing nanotube during the growth process, or remain at the nanotube base, depending on the adhesion between the catalyst particle and thesubstrate. Thermal catalytic decomposition of hydrocarbon has become an active area of research and can be a promising route for the bulkproduction of CNTs. Fluidised bed reactor is the most widely used reactor for CNT preparation. Scale-up of the reactor is the major challenge. [74] [75]CVD is a common method for the commercial production of carbon nanotubes. For this purpose, the metal nanoparticles are mixed with a catalystsupport such as MgO or Al2O3 to increase the surface area for higher yield of the catalytic reaction of the carbon feedstock with the metal particles.One issue in this synthesis route is the removal of the catalyst support via an acid treatment, which sometimes could destroy the original structure ofthe carbon nanotubes. However, alternative catalyst supports that are soluble in water have proven effective for nanotube growth.[76]If a plasma is generated by the application of a strong electric field during the growth process (plasma enhanced chemical vapor deposition), then thenanotube growth will follow the direction of the electric field.[77] By adjusting the geometry of the reactor it is possible to synthesize vertically alignedcarbon nanotubes[78] (i.e., perpendicular to the substrate), a morphology that has been of interest to researchers interested in the electron emissionfrom nanotubes. Without the plasma, the resulting nanotubes are often randomly oriented. Under certain reaction conditions, even in the absence of aplasma, closely spaced nanotubes will maintain a vertical growth direction resulting in a dense array of tubes resembling a carpet or forest.Of the various means for nanotube synthesis, CVD shows the most promise for industrial-scale deposition, because of its price/unit ratio, and becauseCVD is capable of growing nanotubes directly on a desired substrate, whereas the nanotubes must be collected in the other growth techniques. Thegrowth sites are controllable by careful deposition of the catalyst. In 2007, a team from Meijo University demonstrated a high-efficiency CVD techniquefor growing carbon nanotubes from camphor.[79] Researchers at Rice University, until recently led by the late Richard Smalley, have concentrated uponfinding methods to produce large, pure amounts of particular types of nanotubes. Their approach grows long fibers from many small seeds cut from asingle nanotube; all of the resulting fibers were found to be of the same diameter as the original nanotube and are expected to be of the same type asthe original nanotube.[80][edit]Super-growth CVDProcedure PROCEDURE**Do not open the chamber while the alarm red light is on**Never touch the detector (may result in signal off). 1. Obtain a sample from your instructor, place it onto the double-side tape which is then placed on an aluminum sample holder; if you are preparing a powder sample, use a spatula to spread the powder onto the double- side tape. 2. Read the instructions for the Miniflex X-ray diffractometer, which are on the wall above the instrument. Your instructor will explain the operation. 3. Set the instrument at optimum setting as follows
    • time constant 2 range ? chart speed: Low 4. Slide in the sample holder and adjust the beginning 2theta at 70 degree (It scans from high degrees to low degrees) 5. Switch on the start knob and chart recorder (slow) simultaneously, run your sample on slow chart speed. 6. Once scan gets down to 3 degree of 2theta , stop (switch start knob to off) and chart. TURN OFF X-ray. 7. Locate all peaks on the chart and corresponding 2theta values and write their values into the data chart below. Perform the necessary calculations in the table a Data Table of X-ray Diffraction Peaks lattice spacing 2theta theta sin(theta) n d=n x wavelength/sin(theta) =nxd 1 2 3 4 5 6 7 8Wavelength = 1.5418 Å for Cu Ka 8. nd calculate the repeat distance in your unit cell.X-Ray Diffraction ExperimentINTRODUCTIONX-rays are electromagnetic radiation of wavelength about 1 Å (10-10 m), whichis about the same size as an atom. They occur in that portion of theelectromagnetic spectrum between gamma-rays and the ultraviolet. Thediscovery of X-rays in 1895 enabled scientists to probe crystalline structure at
    • the atomic level. X-ray diffraction has been in use in two main areas, for thefingerprint characterization of crystalline materials and the determination oftheir structure. Each crystalline solid has its unique characteristic X-ray powderpattern which may be used as a "fingerprint" for its identification. Once thematerial has been identified, X-ray crystallography may be used to determineits structure, i.e. how the atoms pack together in the crystalline state and whatthe interatomic distance and angle are etc. X-ray diffraction is one of the mostimportant characterization tools used in solid state chemistry amd materialsscience.We can determine the size and the shape of the unit cell for any compoundmost easily using the diffraction of x-rays.Fig. 1 Reflection of x-rays from two planes of atoms in a solid.The path difference between two waves: 2 x wavelength= 2dsin(theta)For constructive interference between these waves, the path difference must bean integral number of wavelengths: n x wavelength= 2x
    • This leads to the Bragg equation: n x wavelength = 2dsin(theta)Figure 2 shows the x-ray diffraction pattern from a single crystal of a layeredclay. Strong intensities can be seen for a number of values of n; from each ofthese lines we can calculate the value of d, the interplanar spacing between theatoms in the crystal.Fig. 2 X-ray diffraction pattern from a layered structure vermiculite clay.EXAMPLE 1 Unit Cell Size from Diffraction DataThe diffraction pattern of copper metal was measured with x-ray radiation ofwavelength of 1.315Å. The first order Bragg diffraction peak was found at anangle 2theta of 50.5 degrees. Calculate the spacing between the diffractingplanes in the copper metal.The Bragg equation is n x wavelength = 2dsin(theta) We can rearrange this equation for the unknown spacing d: d = n x wavelength/2sin(theta).theta is 25.25 degrees, n =1, and wavelength = 1.315Å, and therefore d= 1 x 1.315/(2 x 0.4266) = 1.541 ÅIn this lab you will measure the x-ray powder diffraction pattern from a singlecrystal. Your TA will give you the sample to be measured and show you how toset up the Miniflex x-ray diffractometer.
    • You should measure all the values of 2theta from the chart, and after convertingthem into d values calculate the repeat distance in your unit cell. In your labnote book list all the 2theta values with their corresponding values of n and d.Then calculate the mean and median values of the unit cell.INSTRUMENTATIONThe X-ray diffraction experiment requires an X-ray source, the sample underinvestigation and a detector to pick up the diffracted X-rays. Fig 3 is aschematic diagram of a powder X-ray diffractometer.Fig. 3. Schematic of an X-ray powder diffractometerThe X-ray radiation most commonly used is that emitted by copper, whosecharacteristic wavelength for the K radiation is =1.5418Å. When the incidentbeam strikes a powder sample, diffraction occurs in every possible orientationof 2theta. The diffracted beam may be detected by using a moveable detectorsuch as a Geiger counter, which is connected to a chart recorder. In normal use,the counter is set to scan over a range of 2theta values at a constant angularvelocity. Routinely, a 2theta range of 5 to 70 degrees is sufficient to cover themost useful part of the powder pattern. The scanning speed of the counter isusually 2theta of 2degrees min-1 and therefore, about 30 minutes are needed toobtain a trace.