Monodisperse Double-Walled Carbon Nanotubes Mark C. Hersam, Northwestern University, DMR 0706067

1. Monodisperse Double-Walled Carbon NanotubesMark C. Hersam, Northwestern University, DMR 0706067 Double-walled carbon nanotubes (DWCNTs) are promising materials for a variety of applications due to their exceptional mechanical, thermal, chemical, optical, and electrical properties. However, current synthetic methods yield inhomogeneous mixtures that contain a large proportion of unwanted impurities including single-walled carbon nanotubes, multi-walled carbon nanotubes, and other contaminant species. By exploiting differences in buoyant density, density gradient ultracentrifugation allows DWCNTs to be isolated from as-synthesized raw material. Monodisperse DWCNT samples yield enhanced performance in transparent conductors and help elucidate the fundamental photophysics of DWCNTs. Density gradient ultracentrifugation enables double-walled carbon nanotubes to be isolated from polydisperse as-synthesized raw material. A. A. Green and M. C. Hersam, Nature Nanotechnology, 4, 64 (2009).

2. Presidential Science Debate 2008Mark C. Hersam, Northwestern University, DMR 0706067 The Northwestern University Science Policy Action Network (NU-SPAN) hosted an event entitled “ELECTION 2008: Presidential Perspectives on Science and Technology” on the Northwestern University Campus (Evanston, IL) on October 15, 2008. This debate between representatives from the Obama and McCain campaigns focused exclusively on science and technology policy issues, making it one of only a handful of science policy debates during the 2008 presidential campaign. The debate was moderated by Professor Mark Hersam and was attended by approximately 200 students, faculty, and members of the general public. Professor Mark Hersam serves as the moderator for “ELECTION 2008: Presidential Perspectives on Science and Technology,” Evanston, IL, 10/15/08.

3. Mark C. Hersam, Northwestern University, DMR 0706067 Article abstract Nature Nanotechnology 4, 64 - 70 (2009) Published online: 14 December 2008 | doi:10.1038/nnano.2008.364 Subject Categories: Carbon nanotubes and fullerenes | Electronic properties and devices | Nanomaterials Processing and properties of highly enriched double-wall carbon nanotubes Alexander A. Green1 & Mark C. Hersam1 Abstract Carbon nanotubes consist of one or more concentric graphene cylinders and are under investigation for a variety of applications that make use of their excellent thermal, mechanical, electronic and optical properties. Double-wall nanotubes are ideal systems for studying the interwall interactions influencing the properties of nanotubes with two or more walls. However, current techniques to synthesize double-wall nanotubes produce unwanted single- and multiwall nanotubes. Here, we show how density gradient ultracentrifugation can be used to separate double-wall nanotubes from mixtures of single- and multiwall nanotubes through differences in their buoyant density. This technique results in samples that are highly enriched in either single- or double-wall nanotubes of similar outer wall diameter, with the double-wall nanotubes being, on average, 44% longer than the single-wall nanotubes. The longer average length of the double-wall nanotubes provides distinct advantages when they are used in transparent conductors. Arnold, M.S., Suntivich, J., Stupp, S.I., and Hersam, M.C. "Hydrodynamic Characterization of Surfactant Encapsulated Carbon Nanotubes Using an Analytical Ultracentrifuge." ACS Nano, volume 2, number 11: 2291-2300 (2008).