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Single-walled carbon nanotubes (SWCNT) manufactured with Nano-C's unique combustion technology are currently available in two grades:
- Nano-CAPT: as-produced material (≥ 75% SWCNTs)
- Nano-CPT: purified material (≥ 95% SWCNTs)
The characteristics of each type are described below. For ordering information, please see our product guide. Both product forms can be made into an ink or dispersion (“Nano-C-Ink”) that is ready for customer use as separately described below.
nano-cAPT
As-produced single-walled carbon nanotubes
Fig. 1 Raman spectrum of as-produced combustion-generated material.
Setpoints: 785 nm, laser power: »0.18 mW, exposure time: 4 s, 5 accumulations.
Fig. 2 Scanning electron microscopy (SEM) of as-produced material.
Fig. 3 Transmission electron microscopy (TEM) of as-produced material.
Fig. 4 UV-vis/NIR spectra of as produced SWCNT in a) o-dichlorobenzene
(ODCB) and b) sodium dodecyl sulfate (SDS)/water.
Material generated in the combustion process has been characterized by means of Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Raman spectroscopy confirms the presence of significant amounts of SWCNT (Fig. 1). The G-band occurring in the 1500-1605 cm-1 range corresponding to tangential vibrations indicates an abundance of conducting nanotubes vs. semi-conducting SWCNT. The radial breathing mode (RBM) reflecting the diameter of the detected SWCNT shows combustion generated material to have a narrow diameter distribution. The peak seen in Fig. 1 at a wave number of 220 cm-1 corresponds to a tube diameter of approximately 1.1 nm. The weakness of the peak near 1350 cm-1 (D-band) indicates only low level of impurities or other symmetry-breaking defects. Details about Raman spectroscopy of SWCNT can be found in Dresselhaus et al., Carbon 40 (2002) 2043-2061. Scanning electron microscopy (SEM) has been conducted in the Center of Materials Science and Engineering of the Massachusetts Institute of Technology (MIT) using a JEOL 6320 instrument. Figs. 2a and b show two different locations and magnifications of a randomly selected sample of as-produced material. Bright spots, observed in both images, are thought to be remaining catalyst particles or their reaction products. Different degrees of ordering, partially aligned in Fig. 2a and rather randomly oriented in Fig. 2b can be observed. Transmission electron microscopy (TEM) images of as-produced material are given in Fig. 3a and b. Fig. 3b represents a magnified partial view showing unambiguously the presence of rafts of individual SWCNT. Images have been taken, also at MIT, with a JEOL 2010 instrument. UV-vis/NIR absorption spectra of dispersion in both o-dichlorobenzene (ODCB) and sodium dodecyl sulfate (SDS)/water are shown in Fig. 4. As-produced SWCNT have been dispersed assisted by sonication and followed by centrifugation. Good resolution of spectral features that correspond to electronic transitions specific to SWCNT indicates a high abundance of SWCNT and a high degree of exfoliation.
Nano-C-APT may be used by customers who are not concerned about the presence of metal or metal oxide particles. Easily removable metal and oxide particles typically represent 30 weight % of the as-produced material. As-produced material is also the best choice for customers who worry about effects of purification on the materials composition and/or have developed unique purification methods adapted to their application. One of the features of Nano-C’s process technology is that in producing SWCNTs, no multi-walled structures are observed, and what little amorphous carbon is formed is easily removed.
nano-cPT
Purified single-walled carbon nanotubesTreatment with an oxidative acid or sequences consisting of acid leaching and oxidation lead to nearly quantitative removal of metal, metal oxides and amorphous carbon. Prior to dispersion, a network of SWCNT is formed (Fig. 5). A typical TGA analysis is shown in Figure 6. Purified material is suggested for customers with applications that allow for direct use of high-purity SWCNT. Figure 7a and 7b present selected TEM images.
Fig. 5 Scanning electron microscopy (SEM) of purified material; Fig. 6. Thermogravimetric analysis of purified SWCNT.
Fig. 7a and 7b Transmission electron microscopy (TEM) of purified material.
nano-c-INK
The key innovation in our approach is the ability to produce a range of SWCNT inks (“C-Inks”) suitable for a range of applications without changing the fundamental dispersion chemistry. The different classes of inks are based on physical parameters of the suspended material rather than a different chemical identity. For example, an ink with extensive bundling of SWCNT and hence limited suspendability is still useful for applications such as battery electrodes or capacitors, whereas it is clearly not suitable for a transparent conductive coating application that needs individually suspended SWCNT.
Fig. 8 Interband optical transitions measured in the Nano-C
SWCNT ink. Inset: typical electronic structures of
semi-conducting (bottom, middle) and metallic SWCNT (top)
Nano-C has pioneered the development of an ink using a proprietary formulation based on surfactant free dispersion of purified SWCNT in a water or solvent base. Typically less than 2 V/V% of proprietary molecular additives are used as molecular stabilizers. The key feature of the Nano-C ink is that these stabilizing additives can be removed at a later stage from a SWCNT film by an annealing process at temperatures typically lower than 250°C. Our proprietary stabilizers are capable of suspending purified SWCNT in a water or solvent base to a gravitational force of 25,000G or above for extended periods of time. The resulting ink is stable at ambient conditions meeting shelf life requirements. The competing methods for suspending carbon nanotubes often involve the use of ionic or polymeric surfactants which leads to a non-conducting network of SWCNT (molecular polymer wrapping serving as insulator) or aggressive oxidative conditions resulting in damage to the electronic structure of the tubes. Fig. 8 shows the UV-Vis absorption spectra of a ready to coat, surfactant and polymer free Nano-C-Ink consisting of purified SWCNT (image in the inset).
The ink can be coated on glass, sapphire, and plastic substrates using a number of techniques, including inkjet-printing, spin- or spray-coating, among others, thus serving as a general SWCNT platform for many applications.
Fig. 9 Solutions containing separated semi-conducting
(left) and metallic (right) SWCNT
A SWCNT can be defined as a rolled-up graphene sheet within certain allowed chiralities. Based on this geometric constraint, SWCNT produced by any method statistically will be made up of about 1/3 with metallic and 2/3 with semiconducting behavior . As described above, separation between both material types will enable applications such as thin-film transistors and high-end transparent conducting films.
Nano-C is scaling up technology developed in the laboratory of Prof. Michael Strano in the Department of Chemical Engineering at the Massachusetts Institute of Technology (MIT) for which Nano-C has an exclusive license. These novel materials are available on request. An example of solutions contacting separated semi-conducting and metallic SWCNT is shown in Fig. 9.