Spectroscopy-Based Characterization of Single Wall Carbon Nanotubes

Abstract

We present the initial results of our combined investigation of Raman scattering and optical absorption spectroscopy in a batch of single wall carbon nanotubes (SWNTs). The SWNT diameters are first estimated from the four radial breathing mode (RBM) peaks using a simple relation of . The calculated diameter values are related to the optical absorption peaks through the expressions of first interband transition energies, i.e., for semiconducting and for metallic SWNTs, respectively, where is the carbon-carbon bond length (0.144 nm) andγ is the energy of overlapping electrons from nearest neighbor atoms, which is 2.9 eV for a SWNT. This analysis indicates that three RBM peaks are from semiconducting tubes, and the remaining one is from metallic tubes. The detailed analysis in the present study is focused on these three peaks of the first absorption band by determining the values of the representative (n,m) pairs. The first step of analysis is to construct a list of possible (n,m) pairs from the diameters calculated from the positions of the RBM peaks. The second step is to compute the first interband transition energy, , by substituting the constructed list of (n, m) into the expression of Reich and Thomsen, and Saito et al. Finally, the pairs with the energies closest to the experimental values are selected.

Raman study on single-walled carbon nanotubes with different laser excitation energies

“…Using the equation (Kurti et al 2002), where ω RBM is RBM frequency, d t the tube diameter and A and B are constants, and for bundle A = 234 cm -1 , B = 10 cm -1 , the corresponding tube diameters are 1⋅376, 1⋅3, 1⋅135 and 0⋅966 nm, respectively. Within 5% error range in tube diameters in RBM, as presented earlier by Namkung et al (2004), with no preference in chirality, we find that the sample contains high percentage of semiconducting single-walled carbon nanotubes and this confirms that our sample is of semiconducting type in nature.…”

Method for determination of nature of single-wall carbon nanotubes (SWCNTs) in a bundle prepared by chemical vapor deposition technique

“…Moreover for large tubes (d t > 2 nm) the intensity of RBM feature is weak and is hardly observable. A list of (n, m) pairs for each RBM peak is constructed by allowing an error range and using the expression for tube diameter [5], where a c−c is the carbon-carbon bond length (0.144 nm) and n, m are integers. The list of (n, m) pairs corresponding to the diameters within 5% of 1.135 nm calculated from the RBM peak positions at 216 cm −1 is shown in Table I.…”

“…where a c−c is the carbon-carbon bond length and γ 0 is the nearest-neighbor electronic overlap integral, which is 2.9 eV [10]. Metallic and semiconducting tubes are differentiated by n − m = 3q for semiconducting and n−m = 3q for metallic [5], accordingly the nature of the tube is given in column fifth of Table I. The chiral angle for each chirality is calculated by using the relation θ = tan −1 √ 3m 2n + m [11], and is shown in sixth column of the Table. Seventh column provides the number of carbon atoms per unit cell of a tube defined by (n, m), using the relation 2N = 4(n 2 + m 2 + nm) d r [12], where d r is the greatest common divisor of (2n + m) and (n + 2m).…”

“…However from Raman measurements one can determine the nature of the nanotubes if more than one wavelength is uti-lized [2]. The combined investigation of Raman scattering and optical absorption spectroscopy in a batch of SWNTs was presented by M. Namking et al [5]. It is proposed by H. Kataura et al [6] that within a zone folding scheme one third of SWNTs are metallic and always have a wider energy gaps between spikes than semiconducting ones with almost same diameters.…”

Metallic/semiconducting ratio of carbon nanotubes in a bundle prepared using CVD technique

“…The combined investigation of Raman scattering and optical absorption spectroscopy in a batch of SWNTs was presented by Namkung et al [5] and the authors have made the calculations for one peak position but the actual error range in diameter has been considered to be 15%. In their report [5] no calculation has been made to determine the number of atoms in a unit cell of SWNT, and the chiral angle, which has a pronounced effect on optical properties of SWNTs in a bundle.…”