Chirality Characterization of Dispersed Single Wall Carbon Nanotubes
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J21.2.1
Chirality Characterization of Dispersed Single Wall Carbon Nanotubes Min Namkung1, Phillip A. Williams2, Candis D. Mayweather3, Buzz Wincheski1, Cheol Park4, and Juock S. Namkung5 1 NASA Langley Research Center, Hampton, VA 23681 2 National Research Council, NASA Langley Research Center, Hampton, VA 23681 3 Spelman College, Atlanta, Georgia 30314 4 National Institute of Aerospace, Hampton, VA 23666 5 Naval Air Warfare Center, Patuxent River, MD 20670
ABSTRACT Raman scattering and optical absorption spectroscopy are used for the chirality characterization of HiPco single wall carbon nanotubes (SWNTs) dispersed in aqueous solution with the surfactant sodium dodecylbenzene sulfonate. Radial breathing mode (RBM) Raman peaks for semiconducting and metallic SWNTs are identified by directly comparing the Raman spectra with the Kataura plot. The SWNT diameters are calculated from these resonant peak positions. Next, a list of (n, m) pairs, yielding the SWNT diameters within a few percent of that obtained from each resonant peak position, is established. The interband transition energies for the list of SWNT (n, m) pairs are calculated based on the tight binding energy expression for each list of the (n, m) pairs, and the pairs yielding the closest values to the corresponding experimental optical absorption peaks are selected. The results reveal (1, 11), (4, 11), (5, 12), and (5, 9) among the most probable chiralities for the semiconducting nanotubes. The results also reveal that (4, 16), (6, 12) and (8, 8) are the most probable chiralities for the metallic nanotubes. Directly relating the Raman scattering data to the optical absorption spectra, the present method is considered the simplest technique currently available. Another advantage of this technique is the use of the E11S , E 33S ,and E22M peaks in the optical absorption spectrum in the analysis to enhance the accuracy in the results. INTRODUCTION The physical properties of a single wall carbon nanotube (SWNT) depend on its chirality, which is determined by two integer coefficients, normally denoted by (n, m) [1]. The spectroscopy methods of fluorescence, Raman scattering, and optical absorption have been the mainstream tools for chirality characterization [2-4], and each method has unique capabilities. Fluorescence spectroscopy is a novel technique providing information on the chirality of SWNTs, but its applicability is limited to semiconducting SWNTs. The Raman scattering technique directly provides the distribution of SWNT diameters, which are closely related to the chirality as the diameter of an individual SWNT is determined by its (n, m). Optical absorption spectroscopy provides the interband transition energies, which are also closely related to the chirality distribution since the interband transition energies of a SWNT are an explicit function of its (n, m) values. Unfortunately, both the SWNT diameter and interband transition energy are multivalued functions of (n, m). Hence, it is logical to combine the results of the Raman and optical absorption
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