Work performed on beamlines X18B and x23A2.

1. Selective Synthesis of Subnanometer Diameter Semiconducting Single Wall Carbon Nanotubes Codruta Zoican Loebick, Ramakrishna Podila,‡ Jason Reppert,‡ Joel Chudow,†Fang Ren,† Gary L. Haller,† Apparao M. Rao,‡ and Lisa D. Pfefferle †. † Yale University, Department of Chemical Engineering, ‡Clemson University, Department of Physics. • Single wall carbon nanotubes (SWNT) are one-dimensional systems with exceptional chemical and electronic properties and a vast number of applications. They can be semiconducting or metallic depending on their geometry. A typical sample contains more than 30% metallic component. SWNT are nucleated from catalytic particles. A key factor in the synthesis of SWNT with select geometry and electronic properties is the size and shape of these initiating particles. • Subnanometer diameter SWNT were synthesized by carbon vapor deposition at different temperatures (600, 700, and 800 °C) using CoMn bimetallic catalysts supported on MCM-41 silica templates. The state of the catalyst was investigated using X-ray absorption. EXAFS showed that Co ions are completely reducible under the synthesis conditions and form metallic clusters responsible for SWNT nucleation, while Mn ions which do not reduce act as anchoring sites for narrow Co particle size domains. We find that the size of the metallic particles that seed the growth of sub-nm SWNTs (diameter 0.5-1.0 nm) is highly sensitive to the reaction temperature. The properties of the SWNT were determined from Raman spectroscopy and photoluminescence measurements. Low reaction temperature (600 °C) favors the growth of semiconducting tubes whose diameters range from 0.5 to 0.7 nm. These results were also confirmed by electrical transport measurements. The ratio of semiconducting to metallic SWNT in the samples reacted at the different temperatures increases with decreased reaction temperature. The size of the SWNT generating clusters is smaller at the lower temperatures. • This result is very important as direct catalytic synthesis of semiconducting SWNT is extremely valuable for future electronic applications. C. Zoican Loebick, R. Podila, J. Reppert, J. Chudow, F. Ren, G. L. Haller, A. M. Rao, L. D. Pfefferle, Selective Synthesis of Subnanometer Diameter Semiconducting Single-Walled Carbon Nanotubes, J. Am. Chem. Soc., 132, 11125, (2010) Work performed on beamlines X18B and x23A2.