Preferential Growth of Metallic SWNTs Achieved
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Preferential Growth of Metallic SWNTs Achieved One obstacle to the implementation of single-walled carbon nanotubes (SWNTs) in electronic devices is that their synthesis results in a mixture of conducting and semiconducting species. Progress has been made in separating SWNTs based on their conductivities, which is determined by chirality. Some progress has been made in controlling SWNT structure during growth (e.g., semiconducting SWNTs are produced preferentially by plasma-enhanced chemical vapor deposition), demonstrating that somewhat different mechanisms lead to different chiralities. Recently, A.R. Harutyunyan and co-researchers at the Honda Research Institute, Columbus, Ohio, in collaboration with T.M. Paronyan of the University of Louisville, S.M. Kim of Purdue Uni versity, and their colleagues, were able to increase the fraction of CNTs with metallic conductivity grown from Fe nanocatalysts from 33% to a maximum of 91% by varying the conditions under which the catalyst was annealed. As reported in the October 2 issue of Science (DOI: 10.1126/science.1177599;
Quasicrystalline Order Revealed in Nanoparticle Superlattices Quasicrystals are a class of materials that show sharp diffraction peaks despite presenting forbidden symmetry operations in classical crystallography. D.V. Talapin and M.I. Bodnarchuk from the University of Chicago; E.V. Shevchenko from Argonne National Laboratory; and X. Ye, J. Chen, and C.B. Murray from the University of Pennsylvania, have reported in the October 15 issue of Nature (DOI: 10.1038/nature08439; p. 964) that different binary nanoparticle colloidal systems can self-assemble into 12-fold rotational quasicrystalline order. According to the researchers, the compositional flexibility demonstrated that quasicrystal ordering could be a relatively common phenomenon in nanocrystal solids, with suitable size ratios between particles. Addendum David N. Seidman and Krystyna Stiller, Guest Editors of the theme “A Renaissance in Atom-Probe Tomography” (MRS Bulletin, October 2009), note that in 1973, J.A. Panitz invented the 10-cm atom probe (discussed on p. 745)—now called the imaging atom probe—which is the progenitor of all atomprobe tomographs, citing the following references: J.A. Panitz, Rev. Sci. Instrum. 44, 1034 (1973) and J.A. Panitz, “Field Desorption Spectrometer,” U.S. Patent 3868507 (1975).
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p. 116), Harutyunyan and co-researchers annealed in situ Fe nanocatalysts deposited onto a flat SiO2/Si support, using an ambient atmosphere of He or Ar, and varying ratios of H2 and H2O. Using methane as the carbon source, SWNT synthesis was performed at 860°C. The researchers observed with scanning electron microscopy that increasing the concentration of reductive species (Ar:H2 was increased from 9:1 to 8:2 at 840 Torr with ~3.5 mTorr H2O) during catalyst conditioning resulted in higher densities of SWNTs on the substrate. This led them to perform a systematic study of SWNT growth on catalysts annealed in situ under varying ambient conditions. The ratio of metallic to semiconductin
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