Abstract
Full potential linearized augmented plane waves method with the generalized gradient approximation for the exchange-correlation potential was applied to calculate the optical properties of (7, 7) single walled carbon nanotubes. The both x and z directions of the incident photons were applied to estimate optical gaps, dielectric function, electron energy loss spectroscopies, optical conductivity, optical extinction, optical refractive index and optical absorption coefficient. The results predict that dielectric function, ε (ω), is anisotropic since it has higher peaks along z-direction than x-direction. The static optical refractive constant were calculated about 1.4 (z-direction) and 1.1 (x- direction). Moreover, the electron energy loss spectroscopy showed a sharp π electron plasmon peaks at about 6 eV and 5 eV for z and x-directions respectively. The calculated reflection spectra show that directions perpendicular to the tube axis have further optical reflection. Moreover, z-direction indicates higher peaks at absorption spectra in low range energies. Totally, increasing the diameter of armchair carbon nanotubes cause the optical band gap, static optical refractive constant and optical reflectivity to decrease. On the other hand, increasing the diameter cause the optical absorption and the optical conductivity to increase. Moreover, the sharp peaks being illustrated at optical spectrum are related to the 1D structure of CNTs which confirm the accuracy of the calculations.
Highlights
With the discovery of carbon nanotubes (CNTs), many experimental and theoretical researches have been performed to analyze their properties in different fields
There are three optical band-gaps parallel to the tube axis direction labeled E1, E2 and E3, demonstrate probable direct inter-band transitions between the van Hove singularities (VHs) of the DOS which were equal to 2.2 eV, 3.5 eV and 4 eV respectively
When the diameter of SWCNTs decreases the band-gap increases and the absorption peaks shift to higher photon energies
Summary
With the discovery of carbon nanotubes (CNTs), many experimental and theoretical researches have been performed to analyze their properties in different fields. Since the wave function boundary condition alters with the (n, m) indices called nanotube’s chirality, each SWNT structure has its own optical properties.. Studying the optical properties of CNTs can help to find out their unique structures. We have calculated optical spectrum of [7, 7] carbon nanotubes using FP-LAPW method based on the first-principles density functional theory. The optical properties of SWCNTs have been simulated in various studies.. Several experimental and theoretical studies have considered [7, 7] the carbon nanotubes properties, the optical spectrum of CNTs [7, 7] has not been probed yet The optical properties of SWCNTs have been simulated in various studies. several experimental and theoretical studies have considered [7, 7] the carbon nanotubes properties, the optical spectrum of CNTs [7, 7] has not been probed yet
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