1. Carbon Nanotubes: synthesis, acidic oxidation and application as u ltra sharp and high aspect ratio CNT AFM probes Vaneet Kumar Sharma @Vaneet K Sharma
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3. It was in 1991, Sumio Iijima of the NEC Laboratory, Tsukuba used High Resolution Transmission electron microscope to observe Carbon nanotubes, later in 1993 he observed single walled carbon nanotubes. In his own words it was " Serendipity “, discovery by chance @Vaneet K Sharma
4. Number of different ( n,m ) SWNTs in HiPco C h =na 1 + ma 2 n = m : Metallic (zero band gap) n - m = 3k : Semi-metallic (0.04 eV band gap) n-m ≠ 3k : Semiconducting (0.6~1.2 eV band gap) where k is integer Zigzag Armchair @Vaneet K Sharma
5. Physico-Chemical Large Surface Area (~1600 m 2 /g) Amenable to electrochemical doping Hollow, molecule storage/nanoreactors Thermal conductivity twice as good as diamond (2000 W/m/K) Good thermal stability (750°C in air,) Electrical Metallic or Semiconducting ( 1-D ) met- SWNTs are ballistic conductors (10 9 A/cm 2 ) Mechanical Strongest known fiber (Young’s modulus, ~1 TPa) Highly flexible, Buckle-prone Large aspect ratio (~10 3 ) SWNT Unique Properties @Vaneet K Sharma
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7. Resonance Raman spectroscopy of SWNTs @Vaneet K Sharma Name Position (cm -1 ) Origination (mode) G ’ ~ 2700 Overtone of D-band G 1550-1605 Graphite related mode (A, E 1 , and E 2 ) D ~ 1350 Defect-induced (non-sp 2 ) RBM 400~150 In phase radial displace- ments (A) HiPco SWNTs, E laser = 2.41 eV 500 1000 1500 2000 2500 Wavenumber (cm -1 ) Raman Intensity G ( G + ) D RBM G ’ G ( G - )
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14. Oxidation of single walled carbon nanotubes (SWNTs) SWNTs were sonicated with (sulfuric acid: nitric acid) mixture under Ice bath (0-5 o C), filtered on Buchner funnel and washed with DI water till the pH of Filtered water becomes 7, dried overnight, ~20mg of these oxidised NTs + ~250mg ODA in a vial, were kept at 105C for 5 days, Exfoliation was observed in the oxidized SWNTs, after 5 days, ~20mL THF solvent was aded and sonicated for 1-2 minutes, well dispersed black ink was formed . For Raman studies, sample are drop cast on silicon wafer, annealed at 800 o C (10 o C/min ramp temp.). Resonance Raman characterization was done by using 1.56 ev, 1.96 ev and 2.41ev laser lines HNO 3 +H 2 SO 4 Sonication assisted @Vaneet K Sharma
24. U ltra sharp and high aspect ratio CNT AFM probes by Dielectrophoresis (DEP) Owing to their geometric, electronic, chemical, and mechanical properties, CNT tips offer many advantages in nanoscale imaging and fabrication. The U ltra sharp and high aspect ratio CNT AFM probes that results in a small diameter enables high resolution images of rough surfaces with deep trenches to be taken. Oxidized shortened SWNTs (s-SWNTs) were dispersed in water or DMF with sonication and further diluted to make nanotube solutions with different concentration (0.001~0.01 mg/ml) at which the solution become colorless The deionized water and DMF are chosen as the nanotube dispersion medium whose dielectric constants are 80 and 39 respectively. SWNTs solution used is a mixture of metallic (met-) and semiconducting (sem-) nanotubes, Sem- SWNTs have finite dielectric constant with ε sem < 5 while met- SWNTs are expected to have a very large ε met- owing to the mobile carriers, These tips perform well in the scanning of biological molecules @Vaneet K Sharma
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27. 10X optical microscope 100 X optical microscope SWNTs aqueous solution, 6V, 10seconds Immersion time @Vaneet K Sharma
28. 10V, 20 sec immersion time AFM CNT Tips U ltra sharp and high aspect ratio CNT AFM probes @Vaneet K Sharma
At this point, let me introduce some fundamentals of SWNTs Resonance Raman Sectra which are important in further characterization of SWNTs separations. This a typical 514 nm laser excited RRS spectra from HipCo processed SWNTs. Eventhough small peak features are heavily under study both in theory and experiments, I would like to point our four important peak regions for SWNTs study. G’…. G….c D…. RBM…. Based on the fact, RBM region is strongly depending on diameter, for example, by the shown equation. By correlating the diameter and resonance condition, we can predict the NT types under irradiation. Also G-bands are known to be sensitive for the type of NTs. This is typical G-band from sem- SWNTs. Mainly lorenzean peaks are observed in this case. However, met- SWNTs provides one more specific broad gaussian feature next to the lorenzeans, which is so called BWF shape. Since the G-bands are known to be sensitive for the bundling and other environments, we are mainly concentrating on RBM modes for the characterization of this separation.
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