An investigation into the optimal growth of single-walled carbon nanotubes (SWNTs) in vertical arrays, or carpets, is presented utilizing atomic hydrogen catalyst activation with hot filament chemical vapor deposition. Using acetylene decomposition over Fe catalyst, we study the effect of oxidant-assisted growth using O 2 , CO 2 , and H 2 O. Whereas trace amounts of O 2 result in the lack of any catalytic activity, CO 2 and H 2 O are found to dramatically enhance the catalyst lifetime. On the basis of the saturation effect of oxidant concentration for both CO 2 and H 2 O, we present this as being due to catalyst stabilization from surface hydroxyl groups, with H 2 O having the most dominant effect upon carpet growth. Utilizing water-assisted growth, this process is further optimized to yield high-quality single-walled carbon nanotubes. High temperature growth (∼775 °C) yields the highest-quality SWNTs, whereas controllable growth of double-and few-walled nanotubes can also be achieved at lower temperatures (550-600 °C). Finally, ultralong carpets are demonstrated by utilizing the optimal SWNT growth conditions under an enhanced carbon flux environment.

We present a robust method for synthesis of aligned, single-walled carbon nanotube (CNT) "flying carpets" from nanostructured alumina flakes. Roll-to-roll e-beam deposition is utilized to produce the flakes, and hot filament chemical vapor deposition is utilized to grow dense, aligned carbon nanotubes from the flakes with remarkably high CNT yields. The flakes are captured inside a mesh cage and freely suspended in the gas flow during growth. Optical characterization indicates the presence of high quality, small diameter single-walled carbon nanotubes.

We report the functionalization of individual ultra-short (20–80 nm lengths) single-walled carbon nanotubes (US-tubes) via in situ Bingel cyclopropanation. Upon chemical reduction (K°/THF) of bundled US-tubes, the bundling forces are electrostatically overcome to yield single, negatively charged US-tubes in solution. These single US-tubes can then be functionalized with malonic acid bis-(3-tert-butoxycarbonylaminopropyl) ester using Bingel chemistry (CBr4/DBU) to yield 4–5 adducts nm−1, as determined by x-ray photoelectron spectroscopy (XPS). The derivatized US-tubes remain as individuals after functionalization and charge quenching. Thermogravimetric analysis (TGA) and solid-state NMR spectroscopy confirmed covalent attachment of the adducts and indicated tight wrapping of the adduct arms about the US-tubes. The resulting debundled and derivatized US-tubes serve as a prototype single-molecule-like ‘capsule’ for the containment and delivery of medically-useful payloads.

Vertically aligned carbon nanotubes are grown from Al 2 O 3 -supported Fe-Mo catalyst in a hot filament chemical vapor deposition apparatus. We compare the effect of carbon nanotube growth on deposition of 0.5 and 1 nm thick Fe catalyst layers before and after deposition of 0.1 and 0.2 nm thick layers of Mo. We observe that the order of deposition plays a role in the height of the nanotube arrays, especially evident during growth at elevated reaction pressures where carbon flux is higher. We investigate the role of temperature and pressure on features of the nanotube arrays such as height, alignment, quality, volumetric density, and diameter distribution for each of the catalyst thicknesses and for each case of Fe/Mo and Mo/Fe. We compare our results to those obtained from carpets grown from pure Fe catalyst, and observe that a Mo cocatalyst can be advantageous regardless of how it is deposited. However, we find that the order of deposition plays a key role in the temperature and pressure range in which optimal single-walled carbon nanotube growth occurs.

Properly engineered shortened carbon nanotube "capsules" derived from full-length single-walled carbon nanotubes (SWCNTs) and filled with medical imaging agents offer the opportunity to develop diagnostic contrast agents (CAs) for intracellular molecular imaging. [1,2] Such bioinert carbon nanocapsules, with their imaging-agent cargos safely sequestered within, are lipophilic and intrinsically intracellular agents, even when decorated externally with biocompatible coatings. In this Communication we describe and characterize the first water-soluble CA candidate of this class, designed to be biocompatible in vivo over an extended period of time for computed tomography (CT) X-ray imaging. In comparison, most CT agents in the clinic today are highly hydrophilic and intrinsically extracellular agents designed to clear within hours from the body, largely because of toxicity concerns. With the exception of orally ingested BaSO 4 slurries for gastrointestinal imaging, the commonly employed clinical CAs are based on the 2,4,6-triiodinated-5-aminoisophthalic acid structure (with Iohexol being a common example) [3] where iodine (atomic number, Z = 53) serves as the X-ray-opaque element. Recent advances in Gd 3+-ion [4] and iron oxide [5] filled carbon nanotubes as CAs for magnetic resonance imaging (MRI)has stimulated interest in developing diagnostic imaging agents from nanotube-based materials. Interest in these materials for diagnostic imaging is largely for five reasons: 1) the exterior of nanotubes can be derivatized for biocompatibility and cellular targeting, [6] 2) properly derivatized nanotubes have demonstrated acceptable cytotoxicities for drug delivery, [7,8] 3) nanotubes are relatively bioinert and have been shown to be excreted intact from mammals, [9] 4) derivatized nanotubes readily translocate into mammalian cells, [10] and 5) nanotubes are hollow and can be loaded with metal ions (Gd 3+ for MRI or M n+ radionuclides for nuclear imaging) [4] or small molecules (I 2 for CT imaging) [11][12][13] of medical interest.Collectively, these properties promise the potential for developing carbon-nanotube materials into intracellular agents for molecular imaging, [1] and because of their small size (especially for needlelike ultrashort nanotubes (US-tubes) of ca. 50 nm in length by 1.0 nm in diameter), [14,15] a large number of such agents could accumulate within each targeted cell and thus enhance image intensity. The US-tube material derived from the F 2 cutting of full-length SWCNTs seems ideal because the procedure creates uniform-length nanocapsules (ca. 95 % ≤ 50 nm) with small defects in the sidewalls that serendipitously facilitate a uniform internal loading of ions and small molecules.[4]

Single-walled carbon nanotubes (SWNTs) may be grown from designed seeds containing an SWNT and the catalyst required for continued growth. Dodecyl side-walled functionalized SWNTs (DD-SWNTs) are endfunctionalized with 4-hydroxypyridine via dicyclohexylcarbodiimide coupling to allow covalent coordination of an inorganic cluster pro-catalyst (FeMoC). DD-SWNT-py-FeMoC on spin-on glass was exposed to H 2 / CH 4 at 800 °C, resulting in 3-fold growth in the length of 40% of the seed SWNTs. Only ∼1% of the procatalyst alone nucleate SWNTs under the same conditions, suggesting effective separation of the nucleation and growth processes.

Growth of high quality, vertically aligned single-walled carbon nanotubes (carpets) is achieved using a rapid insertion hot filament chemical vapor deposition (HF-CVD) technique. The effect of the substrate morphology on growth is explored by comparing carpets grown on epitaxially polished MgO substrates to those grown on "as-cut", macroscopically rough MgO substrates. Depending on the substrate morphology, we observe differences in both the overall carpet morphology as well as the diameter distribution of nanotubes grown in the carpet based on optical measurements. In addition, we explore the role of water in the growth of carpets on MgO and the conventional Al2O3 coated Si substrates. We find that the addition of a small amount of water is beneficial to the growth rates of the SWNT carpets, enhancing the growth rates by up to eight times.

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