Small-diameter Single-walled Carbon Research Articles

(Invited) Separation of Small Diameter Swcnts in 1 – 3 Steps with Aqueous Two-Phase Extraction

An aqueous two-phase extraction (ATPE) technique capable of separating small diameter single walled carbon nanotubes in 1, 2 or at the most 3 steps will be presented. Separation is performed in the well-studied two-phase system containing polyethylene glycol (PEG) and dextran but it is achieved without changing the initial concentration or ratio of co-surfactants. Instead, the technique is reliant upon the unique surfactant shell around each nanotube diameter at a fixed surfactant concentration. The methodology to optimize the surfactant to a single set of conditions for the diameter range (0.69 - 0.91 nm) is provided and 11 different chiralities with a purity of 73 – 97% are isolated. These include semiconducting and both armchair and non-armchair metallic nanotube species. Titration of co-surfactant suspensions reveal separation to be driven by the pH of the suspension with each (n,m) species partitioning over a unique pH range. This allows for an (n,m) separation approach to be presented that is as simple as pipetting known volumes of acid into the ATPE system.

Taguchi analysis of parameters for small-diameter single wall carbon nanotube growth

Small diameter single wall carbon nanotubes are desirable for various physical and electrical properties of carbon nanotubes. Here, we report the sensitivities of parameters and the optimal conditions for small diameter carbon nanotube growth by chemical vapor deposition (CVD). These results were obtained using the Taguchi method, which is commonly used to find the optimal parameters of various processes. The possible parameter ranges given by the experimental equipment and laboratory conditions, we attempted several times to determine the proper ranges, using photoluminescence (PL) imaging to determine the exact positions of suspended carbon nanotubes on the quartz substrates after synthesis. The diameters of the carbon nanotubes were then determined from the radial breathing modes (RBM) using Raman spectroscopy with a 785nm wavelength laser. Among the 4 major parameters listed above, we concluded that the temperature was the most significant parameter in determining carbon nanotube diameter, hydrogen flow rate was the second most significant, the ethanol and argon gas flow rate was the third, and finally time was the least significant factor.

Neutravidin-Mediated Extraction of Isolated Small Diameter Single Walled Carbon Nanotubes for Bio-Recognition

Neutravidin-Mediated Extraction of Isolated Small Diameter Single Walled Carbon Nanotubes for Bio-Recognition

Resonance Raman and IR spectroscopy of aligned carbon nanotube arrays with extremely narrow diameters prepared with molecular catalysts on steel substrates.

Carbon nanotubes (CNTs) are considered promising for a large range of emerging technologies ranging from advanced electronics to utilization as nanoreactors. Here we report a controlled facile synthesis of aligned carbon nanotubes with very small dimensions directly grown on steel grid substrates via two-step catalytic chemical vapor deposition (CCVD) of a molecular catalyst (ferrocene) with ethylene as the carbon source. The system is characterized by resonance Raman spectroscopy and the results show single walled carbon nanotube (SWCNT) arrays composed of 0.80 nm to 1.24 nm semiconducting CNTs, as analyzed using Kataura analysis, which is approaching the lowest diameters attainable for SWCNTs. The G+ and G- mode splitting, G- line shapes and ring breathing modes (RBMs) are analyzed to characterize the CNTs. The approach results in close packed and vertically aligned SWCNT bundles formed into hair shapes, with some contribution from multiwall CNTs (MWCNTs). IR spectroscopy is utilized to characterize the edge/defect states that have the ability to form esters and ether bonds in the as-prepared CNTs. The stepwise deposition of the catalyst followed by the carbon source gives control over the formation of small diameter single walled carbon nanotubes (SWCNTs). The utilization of molecular catalysts for narrow diameter growth directly on steel grid substrates forms a promising approach for producing cost-effective CNT substrates for a plethora of sensing and catalytic applications.

Single-wall carbon nanotubes as coherent plasmon generators

The possibility of low-energy surface plasmon amplification by optically excited excitons in small-diameter single wall carbon nanotubes is theoretically demonstrated. The nonradiative exciton-plasmon energy transfer causes the buildup of the macroscopic population numbers of coherent localized surface plasmons associated with high-intensity coherent local fields formed at nanoscale throughout the nanotube surface. These strong local fields can be used in a variety of new optoelectronic applications of carbon nanotubes, including near-field nonlinear-optical probing and sensing, optical switching, enhanced electromagnetic absorption, and materials nanoscale modification.

A combined photoemission and ab initio study of the electronic structure of (6,4)/(6,5) enriched single wall carbon nanotubes

AbstractDue to the growing number of applications of small diameter single wall carbon nanotubes (SWCNTs) in opto‐electronics and biological imaging, there is a strong need for a better understanding of their electronic properties. Because (6,5) tubes with a diameter of 0.75 nm are currently the strongest enriched in the CoMoCat synthesis process, they are one of the most studied carbon nanotubes. However, there is still a lack of knowledge on the electronic properties of these tubes. In this paper, we report on a detailed analysis of the electronic structure of (6,4)/(6,5) enriched nanotubes with a combined experimental and theoretical approach. From photoemission the detailed C1s and valence band response of these narrow diameter tubes is studied. The observed electronic structure is in sound agreement with state of the art ab initio calculations using density functional theory.

Preferred functionalization of metallic and small-diameter single walled carbon nanotubes via reductive alkylation

A selectivity investigation of the covalent sidewall functionalization of SWNTs by reductive alkylation (Billups reaction) is reported. The functionalized tubes Rn-SWNT were characterized by UV-vis-nIR absorption, nIR emission and Raman spectroscopy. The reduction of SWNTs with sodium and the subsequent alkylation of the reduced tubes SWNTn− with butyl iodide reveal a pronounced SWCNT diameter dependence, that is, SWNTs with smaller diameter are considerably more reactive than tubes with larger diameter. Moreover, this reaction sequence also favours the preferred functionalization of metallic over semiconducting tubes. Treatment of the reduced intermediates SWNTn− with protons, via the use of ethanol, instead of alkyl iodide leads to hydrogenated tubes. However, in this case the degree of functionalization is considerably lower than that observed for the corresponding alkylation. Also no pronounced preference of the reaction of metallic and small diameter tubes was observed during the hydrogenation process.