10. Nanotubes have been constructed with high length-to-diameter ratio of up to 28,000,000:1
11. These cylindrical carbon molecules have novel properties that make them potentially useful in many applications in nanotechnology, electronics, optics and other fields of materials science, as well as potential uses in architectural fields.
16. They can be twisted, flattened and bent into small circles or around sharp bends without breaking, and severe distortions to the cross-section of nanotubes do not cause them to break.
17. This Flexibility is generally understood by the uniform distribution and propagation of pressure along the tube.
19. An individual -elastic modulus ~ 1 TPa, For bundles 15-20 nm in dia ~ 100 Gpa. Electronic,Thermal & Mechanical Properties of Carbon Nanotubes
20.
21. Mechanical Properties cont.. How to test ????? 7 Impact Testing (a) 3D rendering of an AFM image of a SWNT bundle adhered to the alumina ultra filtration membrane, leading to a clamped beam configuration for mechanical testing. (b) Schematic representation of the measurement technique. The AFM applies a load, F, to the portion of nanotube with a suspended length of L and the maximum deflection d at the center of the beam is directly measured from the topographic image, along with L and the diameter of the tube (measured as the height of the tube above the membrane) Electronic,Thermal & Mechanical Properties of Carbon Nanotubes
22. 8 Mechanical Prop.Cont… Young’s Modulus & Disorder Correlation of the measured Youngs modulus of MWNTs with the amount of disorder present with the graphitic walls. (A) Ranges of measured moduli for three different types of MWNT against an arbitrary scale of increasing disorder. (B) The amount of disorder seen in HRTEM data can be qualitatively ranked to make the correlation. MWNTs were produced via, i) arc-discharge, and decomposition ofacetylene using a Co / silica catalyst, ii) at 720oC and iii) at 900oC. All scale bars are 10 nm. Electronic,Thermal & Mechanical Properties of Carbon Nanotubes
23. Mechanical Prop Cont… 9 Adapted From : Elastic Properties of Carbon Nanotubes and Nanoropes, PHYSICAL REVIEW LETTERS 18 AUGUST 1997VOLUME 79, NUMBER 7 Electronic,Thermal & Mechanical Properties of Carbon Nanotubes
24. 10 Mechanical Properties Cont… Adapted From : Elastic Properties of Carbon Nanotubes and Nanoropes, PHYSICAL REVIEW LETTERS 18 AUGUST 1997VOLUME 79, NUMBER 7 Electronic,Thermal & Mechanical Properties of Carbon Nanotubes
25. Electrical Properties Current capacity Carbon nanotube 1 GAmps / cm2 Copper wire 1 MAmps / cm2 Unique electronic properties - due to the quantum confinement of electrons normal to the nanotube axis. Around the circumference of the nanotube, periodic boundary conditions come into play. Axial Propagation of electrons- The resulting number of one-dimensional conduction and valence bands effectively depends on the standing waves that are set up around the circumference of the nanotube. The choice of n and m determines whether the nanotube is metallic or semiconducting, All variation due to K Point. Since the band gap in semiconducting nanotubes is inversely proportional to the tube diameter, the band gap approaches zero at large diameters, just as for a graphene sheet. At a nanotube diameter of about 3 nm, the band gap becomes comparable to thermal energies at room temperature. SWNT - prototypes of 1d conductors.- But not MWNT 11 Electronic,Thermal & Mechanical Properties of Carbon Nanotubes
26. 12 Electrical Properties cont.. Effect of Structure on electronic States of CNT Schematic structures of SWNTs and how they determine the electronic properties of the nanotubes. (a) A (10,10) arm-chair nanotube. Bottom panel: the hexagon represents the first Broulloin zone of a graphene sheet in reciprocal space. The vertical lines represent the electronic states of the nanotube. The center-line crosses two corners of the hexagon, resulting in a metallic nanotube. (b) A (12, 0) zigzag nanotube. The electronic states cross the hexagon corners, but a small band gap can develop due to the curvature of the nanotube. (c) The (14, 0) zigzag tube is semiconducting because the states on the vertical lines miss the corner points of the hexagon. (d) A (7, 16) tube is semiconducting. This figure illustrates the extreme sensitivity of nanotube electronic structures to the diameter and chirality of nanotubes Electronic,Thermal & Mechanical Properties of Carbon Nanotubes
27. 13 Electrical Properties cont.. At low temperatures step-like current-voltage characteristics are obtained that indicate single-electron transport with Coulomb blockade and tunnelling effect. Electronic,Thermal & Mechanical Properties of Carbon Nanotubes
28. 14 Electrical Properties cont. Connecting SWNTs Connecting SWNTs to the macroscopic world for electrical measurements. (a) AFM image of a SWNT contacted by metal electrodes (bright regions at the left and right of the image). (b) AFM image of two crossing nanotubes each connected to two metal electrodes (courtesy of Dr. P. McEuen). (c) AFM image of a nanotube heterojunction formed by a metallic tube connected to a semiconducting tube (courtesy of Dr. C. Dekker and Z. Yao). Electronic,Thermal & Mechanical Properties of Carbon Nanotubes
29. 15 Electrical and Electronic Properties : Some Observations Electrical properties of individual SWNTs. (a) Resistance as a function of temperature for a metallic SWNT contacted by two Ti electrodes. (b) I–V curves for a semiconducting SWNT under various gate voltages Vg. The gate voltage is applied to the sample substrate as illustrated in the inset below. (c) I vs. Vg characteristics for the nanotube. The inset shows the schematic sample configuration. The metal-contacted nanotube device with source (S) and drain (D) electrodes is fabricated on a 500 nm thick silicon oxide surface. The silicon substrate underneath the silicon oxide is highly doped and electrically conducting. Electronic,Thermal & Mechanical Properties of Carbon Nanotubes
30.
31. Nanotube may be a true one-dimensional metal or a semiconductor with a gap. By combining metallic and semiconducting tubes the whole span of electronic components ranging from wires, bipolar devices to field-effect transistors may be embodied in nanotubes
32. Because MWNTs consists of several concentrically arranged SWNTs, one would expect that MWNTs do not qualify as 1d conductors.
33. The capacitance of a nanotube scales linearly with the inverse of its length. For a micron long nanotube, the single-electron charging energy is sufficiently high for the Coulomb blockade to be observed at liquid helium temperature 4.2 K
34. These nanotubes exhibit transistor behavior at room temperature, that is, their conductance can be changed dramatically (by orders of magnitude) by gate voltage
35. Intra Molecular Junctions – building Blocks of Future electronics Metal – Semiconductor Junction – Molecular Diode Metal Metal Junction – Very low conductivity - As an ohmic element Electronic,Thermal & Mechanical Properties of Carbon Nanotubes
36. 17 Electronic Properties cont… Nanotube contact with Al as gate and gold Substrate Model of a nanotube junction. Note the 5- and 7-ring that are highlighted in orange. The tube segment at the top can for example be metallic whereas the bottom segment is semiconducting. Electronic,Thermal & Mechanical Properties of Carbon Nanotubes
37. 18 Electronic Properties Cont.. Across metallic SWNTs it was found that the voltage drop along the length of the nanotube is very small . These results all point to ballistic transport with minimum electron scattering in metallic SWNTs. I-V characteristics for a single closed and opened MWNT (the current is given in logarithmic scale), and corresponding TEM micrographs of typical NT tips Electronic,Thermal & Mechanical Properties of Carbon Nanotubes
38. Electronic Properties Cont … 19 Variation of Conductance with voltage of p type semiconductor nanotube i-v characteristics at different Gate Voltages for p type SWNT FET. Electronic,Thermal & Mechanical Properties of Carbon Nanotubes
39. Thermal Properties of Carbon Nanotubes Electronic,Thermal & Mechanical Properties of Carbon Nanotubes 20 All nanotubes are expected to be very good thermal conductors along the tube, exhibiting a property known as "ballistic conduction," but good insulators laterally to the tube axis. It is predicted that carbon nanotubes will be able to transmit up to 6000 Watt Per M Per K at room temperature; compare this to copper, a metal well-known for its good thermal conductivity, which transmits 385 W·m−1·K−1. The temperature stability of carbon nanotubes is estimated to be up to 2800 °C in vacuum and about 750 °C in air.
52. The sharpness deteriorates with increasing energy, and that many nanotubes have very similar E22 or E11 energies, and thus significant overlap occurs in absorption spectra.
53. This overlap is avoided in photoluminescence mapping measurements , which instead of a combination of overlapped transitions identifies individual (E22, E11) pairs.
63. Electrical Transport Properties and Field-Effect Transistors of Carbon Nanotubes, Hongjie Dai*, Ali Javey, Eric Pop, David Mann and Yuerui Lu NANO: Brief Reports and Reviews ,Vol. 1, No. 1 (2006) 1–4
64. Single-Walled Carbon Nanotube Electronics,Paul L. McEuen, Michael S. Fuhrer, and Hongkun Park IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 1, NO. 1, MARCH 2002
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