title: Raman characterization of single-walled nanotubes of various diameters obtained by catalytic disproportionation of CO.
abstract: Single-walled carbon nanotubes prepared by disproportionation of CO over Co-Mo/SiO2 catalysts have been characterized by Raman spectroscopy, using several excitation energies. By varying the reaction temperature, different ranges of nanotube diameter were obtained. The average diameter of a single-walled nanotube produced at 750 degrees C was 0.9 nm, while it increased up to about 1.5 nm when the synthesis was conducted at 950 degrees C. The analysis of the Raman spectra obtained with a range of laser excitation energies not only gives a definite description of the single-walled nanotubes diameters but also helps differentiate the metallic or semiconducting character of the samples. This analysis can be done by comparing the experimental data with calculated gap energies as a function of nanotube diameter as well as comparing the relative intensity of bands centered at 50-60 cm-1 lower than the tangential G mode. The analysis of this feature, which can be fitted with a Breit-Wigner-Fano line, offers a method for distinguishing between metallic and semiconducting single-walled carbon nanotubes.
authors.affiliation: School of Chemical Engineering and Materials Science, University of Oklahoma, Norman, Oklahoma, USA.
authors.forename: J E
authors.initials: JE
authors.lastname: Herrera
authors.forename: L
authors.initials: L
authors.lastname: Balzano
authors.forename: F
authors.initials: F
authors.lastname: Pompeo
authors.forename: D E
authors.initials: DE
authors.lastname: Resasco
mesh_terms: D002248:Carbon Monoxide / Q000737:chemistry; D002384:Catalysis; D003035:Cobalt / Q000737:chemistry; D003460:Crystallization / Q000379:methods*; D006358:Hot Temperature; D008422:Materials Testing / Q000379:methods*; D008670:Metals / Q000737:chemistry; D008968:Molecular Conformation; D008982:Molybdenum / Q000737:chemistry; D036103:Nanotechnology / Q000379:methods; D037742:Nanotubes, Carbon / Q000737:chemistry* / Q000145:classification* / Q000302:isolation & purification; D012666:Semiconductors; D012822:Silicon Dioxide / Q000737:chemistry; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013499:Surface Properties; D013696:Temperature
chemical_list: D008670:Metals; D037742:Nanotubes, Carbon; D003035:Cobalt; D012822:Silicon Dioxide; D002248:Carbon Monoxide; D008982:Molybdenum