lecture15 - 2.57 Nano-to-Macro Transport Processes Fall...

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2.57 Nano-to-Macro Transport Processes Fall 2004 - Lecture 15 Guest lecture by Prof. Dresselhaus 1. Outline -Overview -Synthesis -Structures and Symmetry -Electronic Properties -Transport Properties -Phonon Properties -Resonant Raman Effect -Applications 2. Unique Structure and Properties of Single Wall Carbon Nanotubes (SWNTs) A SWNT can be viewed as a cylinder formed by rolling up a graphene sheet. Image removed for copyright reasons. A SWNT is an ideal model of 1D systems for nanoscience. It has the following interesting characteristics: (1) Size SWNTs are nanostructures with dimensions of ~1 nm diameter (~20 atoms around the cylinder). The smallest SWNT has a diameter of only 0.4 nm. (2) Electronic Properties They can be either metallic or semiconducting depending on the diameter or orientation of the hexagons. (3) Mechanical SWNTs have very high strength, Young’s modulus, and good properties on compression and extension. SWCNs can be used to make heat pipes and electromagnetic antennas. Its structure can be determined by single nanotube (as one molecule) spectroscopy. Due to the unique properties, currently many applications are being attempted worldwide for CNs. 2.57 Fall 2004 – Lecture 15 1
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3. Synthesis Three methods are utilized to grow CNs: (1) Arc Discharge In the following figure, two graphite rods (5-20 mm in diameter) are used as the cathode and anode, between which arcing occurs when 50-120A DC is supplied. By electron collision into the anodic rod, carbon clusters from the anodic graphite rod are condensed on the surface of the cathodic graphite rod and carbon nanotubes are formed along with other products. Image removed for copyright reasons. Y. Saito et al, Phys. Rev . 48 1907 (1993) (2) Laser Ablation The experimental setup is shown as following, where Nd-Yb-Al-garmet Laser is utilized at 1200 . Image removed for copyright reasons. A. Thess et al. Science 273 483 (1996) 2.57 Fall 2004 – Lecture 15 2
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For the laser ablation method, we always get many twisted “wires”, which are bundles of SWCNs and thus difficult to use. Isolated single wall carbon nanotubes can be by grown by the Chemical Vapor Deposition (CVD) method. By depositing catalyst on the specified positions, we can control the location of grown CNs. This brings tremendous convenience to the research. Some work has also been conducted to control the average diameter and diameter distribution by changing the catalysts and furnace temperature (H. Kataura et al., 2000). Image removed for copyright reasons. N. Wang et al. Nature 408, 50 (2000) The above figure shows the smallest SWNT with a diameter 0.42 nm. It is a (5,0) zigzag nanotube and has metallic electronic structure. Under 15 K it becomes a superconductor. Image removed for copyright reasons.
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This note was uploaded on 01/12/2011 for the course ME 305 taught by Professor Wright,j during the Spring '10 term at Birla Institute of Technology & Science, Pilani - Hyderabad.

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lecture15 - 2.57 Nano-to-Macro Transport Processes Fall...

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