Single mode phonon energy transmission in functionalized carbon nanotubes

Abstract

Although the carbon nanotube (CNT) features superior thermal properties in its pristine form, the chemical functionalization often required for many applications of CNT inevitably degrades the structural integrity and affects the transport of energy carriers. In this article, the effect of the side wall functionalization on the phonon energy transmission along the symmetry axis of CNT is studied using the phonon wave packet method. Three different functional groups are studied: methyl (-CH(3)), vinyl (-C(2)H(3)), and carboxyl (-COOH). We find that, near Γ point of the Brillouin zone, acoustic phonons show ideal transmission, while the transmission of the optical phonons is strongly suppressed. A positive correlation between the energy transmission coefficient and the phonon group velocity is observed for both acoustic and optical phonon modes. On comparing the transmission due to functional groups with equivalent point mass defects on CNT, we find that the chemistry of the functional group, rather than its molecular mass, has a dominant role in determining phonon scattering, hence the transmission, at the defect sites.

Single mode phonon scattering at carbon nanotube-graphene junction in pillared graphene structure

“…20 Second, Figure 4 contradicts the direct correlation between phonon group velocity and energy transmission coefficient, which has been repeatedly confirmed in various CNT systems. [11][12][13][14]17 It is observed, however, that the LA mode transmission still retains the group velocity correlation feature as shown in Figure 5, where the transmission of LA mode is the least when its group velocity is the slowest. However, the LA phonon transmission is still quite weak near C point, contrary to what has been previously observed in other related studies of CNT phonon transmission.…”

“…Phonon dynamics and the energy transmission have been extensively studied for CNT systems with small scale defects, 11,12 side-wall functionalization, 13 and vertically linked CNTs. 14 The accumulated understanding provides a few general characteristics of CNT phonon scattering; such as a direct correlation between phonon energy transmission and phonon group velocity, and the nearly ideal transmission of the low wave number acoustic phonons.…”

“…14 The accumulated understanding provides a few general characteristics of CNT phonon scattering; such as a direct correlation between phonon energy transmission and phonon group velocity, and the nearly ideal transmission of the low wave number acoustic phonons. 12,13 However, phonon scattering at the junction structure of a hierarchical nanostructure has not been addressed yet.…”

“…13,[15][16][17] In essence, this method is a classical MD simulation with carefully prepared initial conditions. The initial displacements of atoms from their classical ground microstate prescribe the localized lattice vibration of a specific polarization and wave vector.…”

“…19 So far, most of the CNT phonon transmission studies report a few common features such as a direct correlation between phonon group velocity and energy transmission coefficient, the strong reflection of optical phonons near C point of the Brillouin zone (BZ), and the almost ideal transmission of acoustic phonons near C point. [11][12][13] One notable exception is the high frequency phonon filtering feature, reported for vertically linked CNTs. 14 The CNT-graphene junction, however, presents surprisingly different phonon scattering characteristics.…”