About six years ago, the international ISO Standards Committee began emphasizing carbon nanotubes and related materials as a prototype material for establishing nanometrology standards. These standards are needed in order to transition the achievements in nanoscience to nanotechnology. Due to the different properties exhibited by materials in bulk form as compared to the nanoscale, the research community recognizes the need for establishing metrology on the nanoscale level. In view of this need, the International Conference on Carbon Nanotubes established a satellite series of workshops on this topic. The Sixth International Workshop on Metrology, Standardization and Industrial Quality of Nanotubes (MSIN13) took place in Tallinn, Estonia, on June 29.
For synthesis and processing, the advances on separation of single-walled carbon nanotubes by diameter, metallicity, and chiral angle show that chemistry has a key role in adding value to nanotechnology. It appears that separation is no longer the cost limit of carbon nanotube products. Further reduction in manufacturing costs for bulk production is needed. In this context, exfoliation of graphene from natural graphite may have an advantage.
Separation procedures by diameter and chirality are likely to play an important role in the development of standard reference materials for characterizing nanotubes. Interestingly, the application of carbon-related standards can be used for developing nanometrology in general, with graphene being proposed as a reference material for characterizing the limiting properties of focused ion-beam devices, which were widely used for nanopatterning.
On the issue of quality and evaluation protocols, characterization protocols proposed in early reports of MSIN meetings are already being considered as standard techniques, as they are being broadly used for purity and quality evaluation. Commonly used characterization techniques are electron microscopy, thermo gravimetric analysis, Raman spectroscopy, and optical absorption spectroscopy. X-ray photoelectron spectroscopy has been used to quantify very low concentrations of dopants (below 1% in weight). The ISO TC229 has made great progress on standardizing these tools.
On the development of new metrology tools, various optical techniques provide fast and noninvasive methods. While optical absorption and Raman spectroscopy can already be considered standard methods, new techniques are pushing the limits, such as tip-enhanced Raman spectroscopy, nonlinear optics, plasmonics, and photocurrent spectroscopy. Graphene, again, was discussed because the use of isotope metrology on this material allowed the identification of the signal from specific layers in a multilayer sample and enhanced the understanding of the structure and properties of graphite intercalation compounds.
Overall, the nanotube field needs further development from a metrology standpoint. Further work is needed to speed the development of metrology, especially with regard to the application of carbon nanotube materials in biology, medicine, and issues related to toxicology.
