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NanoPower Research Labs

Carbon Nanotubes

SEM Image of SWCNT

Single wall carbon nanotubes (SWCNT) can be envisioned as a rolled up graphene sheet into a seamless cylinder with fullerene caps. The van der Waals interaction between sidewalls leads to close-packed “bundles,” which are an important physical property and the dimensions can be observed in a scanning electron micrograph. The role-up vectors from a point of origin on a graphene sheet will determine the so-called "chirality" of the SWCNT, which determines whether the structure will be metallic or semiconducting. The optoelectronic properties of a SWCNT will depend directly on the chiral angle and diameter of the nanotube. The optical spectra become unique “signatures” for each SWCNT, and in the case of semiconducting SWCNTs, band gap energies inversely proportional to diameter are observed typically between 0.5-1.0 eV and the use of optical absorption spectroscopy can distinctly monitor these effects. SWCNT spectroscopy is a core strength of the NPRL with capabilities including high resolution SEM, near-IR fluorescence spectroscopy, optical absorption spectroscopy, Raman spectroscopy, and thermogravimetric analysis, among others. The NPRL is investigating the uses of SWCNTs in a number of applications including conductive wires, Li-ion battery electrodes, thermionic emitters, transparent conductive coatings, and additives in bulk-heterojunction organic photovoltaics. The NPRL produces and purifies their own material using laser vaporization synthesis, and chemical refluxing, respectively.

(a) chirality chart depicting the multitude of (n, m) SWCNT structures possible based on the role-up vectors. (b) (top) optical absorption spectrum for SWCNTs and (bottom) “Kataura Plot” of the electronic transitions for SWCNTs. The spectrum is a convolution of the diameter distribution for the sample (shown by the gray box). (c) Depiction of the electronic density of states for a semiconducting nanotube based upon a free-electron model which shows the “spikes” due to 1-dimensional quantum confinement. (d) Schematic of the excitonic model for SWCNT absorption and fluorescence processes whereby odd (u) states are 1-photon active and even (g) states are 1-photon inactive.

Multi-walled carbon nanotubes (MWCNTs) are carbon nanotubes comprised of multiple “rolled-up” graphene sheets in concentric cylinders. Many of the structural properties are similar to that of SWCNTs, however; due to the many concentric layers, most MWCNTs are metallic-like conductors and do not have the same discrete bound states or characteristic optoelectronic properties. Other techniques, such as Raman spectroscopy, have routinely been used to investigate the properties (e.g., purity) of the MWCNT materials. MWCNTs are a slightly less expensive alternative to high-purity SWNCTs as they can be produced at a greater rate and can perform nearly as well in applications such as free standing electrodes or as conductive additives in polymer composites. The NPRL synthesizes MWCNTs using a CVD reactor developed in-house and subsequently utilize the resulting materials in applications includeing Li-ion batteries, proton exchange membrane fuel cells, and bulk heterojunction organic photovoltaics.

Recent Publications:
Landi, B.J.; Raffaelle, R.P.; Heben, M.J.; Alleman, J.L.; VanDerveer, W.; and Gennett, T. “Single Wall Carbon Nanotube-Nafion Composite Actuators.” Nano Lett. 2002, 2, 1329.
Landi, B.J.; Raffaelle, R.P.; Heben, M.J.; Alleman, J.L.; VanDerveer, W.; and Gennett, T. “Development and Characterization of Single Wall Carbon Nanotube-Nafion Composite Actuators.” Mater. Sci. Eng. B. 2005, 116, 359-362.
Raffaelle, R.P.; Landi, B.J.; Harris, J.D.; Bailey, S.G.; Hepp, A.F. “Carbon Nanotubes for Power Applications.” Mater. Sci. Eng. B. 2005, 116, 233-243.

» SWCNT Synthesis

» MWCNT Synthesis

» Material Characterization

» Carbon Nanotube Electrodes for batteries and fuel cells

» Single Wall Carbon Nanotube Wire Harness

 


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