Abstract
In this work, the Raman spectra of LCCs encapsulated single-walled carbon nanotubes (SWCNTs) are calculated using the spectral moment’s method. To derive the optimum configurations of the linear carbon chains inside nanotubes, the minimum energy calculations using a convenient Lennard-Jones expression of the van der Waals intermolecular potential is devoted. The optimized structures show that the minima correspond to nanotubes configurations with diameter close to 0.68nm. The influence of the nanotube diameter and chirality are investigated. We also address the important question of the effect of filling degree using the frequency of Raman active modes. These predictions are useful to interpret the experimental data.
Highlights
Since their first observation in 1991 by Iijima, carbon nanotubes (CNTs) have drawed in enormous attention of both experimentalists and theoreticians
The polarized Raman spectrum of single-walled carbon nanotubes (SWCNTs) is significantly dominated by Tangential Mode (TM) situated between 1400 and 1600 cm−1 and by the RBM lower than 400 cm−1
A lot of experimental and theoretical Raman studies have shown that the TM region is mainly sensitive to the tube chirality, while the wavenumber of the RBM downshifts as the tube diameter increases according to the relation ω = A, D
Summary
Since their first observation in 1991 by Iijima, carbon nanotubes (CNTs) have drawed in enormous attention of both experimentalists and theoreticians. The Raman spectra of LCCs (Polyyne: C2nH2 n=2-30) encapsulated in single-walled carbon nanotubes (SWCNTs) are calculated by the spectral moment method.[4,5] using a different size of the polyyne molecules and the diameter distribution of the SWCNTs. The structure of the LCCs inside SWCNTs (LCC@SWCNT) are first optimized. The energy minimization of the different hybrid systems is performed and the configuration of encased polyyne molecules inside SWCNTs is obtained to adopt a linear structure along tube's long axis. These results are consistent with those from Chang et al [6]who showed using DFT that LCCs molecules form a linear chain along the (5,5) and (8,0) SWCNTs axis. Is used to describe the LCC-tube interactions with parameters: σ=3.407Å and ε=0.002964 eV
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