Limits...
Low thermal conductivity in ultrathin carbon nanotube (2, 1).

Zhu L, Li B - Sci Rep (2014)

Bottom Line: Detailed lattice dynamic calculations suggest that the acoustic phonon modes greatly soften in CNT (2, 1) as compared to regular CNTs.Moreover, both phonon group velocities and phonon lifetimes strikingly decrease in CNT (2, 1), which result in the remarkable reduction of thermal conductivity.Besides, isotope doping and chemical functionalization enable the further reduction of thermal conductivity in CNT (2, 1).

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Centre for Computational Science and Engineering, and Graphene Research Center, National University of Singapore, Singapore 117542, Republic of Singapore.

ABSTRACT
Molecular dynamic simulations reveal that the ultrathin carbon nanotube (CNT) (2, 1) with a reconstructed structure exhibits a surprisingly low thermal conductivity, which is only ~16-30% of those in regular CNTs, e.g. CNT (2, 2) and (5, 5). Detailed lattice dynamic calculations suggest that the acoustic phonon modes greatly soften in CNT (2, 1) as compared to regular CNTs. Moreover, both phonon group velocities and phonon lifetimes strikingly decrease in CNT (2, 1), which result in the remarkable reduction of thermal conductivity. Besides, isotope doping and chemical functionalization enable the further reduction of thermal conductivity in CNT (2, 1).

No MeSH data available.


Related in: MedlinePlus

(a) Group velocities, (b) phonon lifetimes, and (c) frequency resolved thermal conductivity distributions in CNT (2, 1) and (2, 2).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4017211&req=5

f4: (a) Group velocities, (b) phonon lifetimes, and (c) frequency resolved thermal conductivity distributions in CNT (2, 1) and (2, 2).

Mentions: The direct consequence of phonon softening is the reduction in group velocities. To quantitatively compare the group velocities (vg) of phonons in CNT (2, 1) and (2, 2), we calculate them according to Hellmann-Feynman theorem, where D, eph, and ω are dynamic matrix, phonon eigenvector, and eigen-frequency, respectively. The obtained group velocities of phonons in both CNT (2, 1) and CNT (2, 2) are drawn in Figure 4a. In the intermediate and high frequency region, i.e., >18 THz, the phonon group velocities in CNT (2, 1) are comparable to or slight smaller than those in CNT (2, 2). But in the low-frequency region, the group velocities of phonons in CNT (2, 1) are much smaller than those in CNT (2, 2), for example, the sound velocity of longitudinal acoustic (LA) phonon is about ~22 km/s in CNT (2, 2), while it is plummeted to ~15 km/s in CNT (2, 1). The reduction of group velocities will strongly lower the thermal conductivity. The contribution of phonon mode (q, ν) to the total thermal conductivity can be expressed as where Cph(q, ν), vg(q, ν) and τ(q, ν) are volumetric specific heat, group velocity, and lifetime of the phonon mode (q, ν) (q and ν denote the phonon wavevector and the index of phonon branch, respectively), respectively; and N is the total number of q points. Considering the fact that the acoustic phonon modes are usually major energy carriers in thermal transport, the reduced group velocities of acoustic phonon modes in CNT (2, 1) will remarkably reduce its thermal conductivity.


Low thermal conductivity in ultrathin carbon nanotube (2, 1).

Zhu L, Li B - Sci Rep (2014)

(a) Group velocities, (b) phonon lifetimes, and (c) frequency resolved thermal conductivity distributions in CNT (2, 1) and (2, 2).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4017211&req=5

f4: (a) Group velocities, (b) phonon lifetimes, and (c) frequency resolved thermal conductivity distributions in CNT (2, 1) and (2, 2).
Mentions: The direct consequence of phonon softening is the reduction in group velocities. To quantitatively compare the group velocities (vg) of phonons in CNT (2, 1) and (2, 2), we calculate them according to Hellmann-Feynman theorem, where D, eph, and ω are dynamic matrix, phonon eigenvector, and eigen-frequency, respectively. The obtained group velocities of phonons in both CNT (2, 1) and CNT (2, 2) are drawn in Figure 4a. In the intermediate and high frequency region, i.e., >18 THz, the phonon group velocities in CNT (2, 1) are comparable to or slight smaller than those in CNT (2, 2). But in the low-frequency region, the group velocities of phonons in CNT (2, 1) are much smaller than those in CNT (2, 2), for example, the sound velocity of longitudinal acoustic (LA) phonon is about ~22 km/s in CNT (2, 2), while it is plummeted to ~15 km/s in CNT (2, 1). The reduction of group velocities will strongly lower the thermal conductivity. The contribution of phonon mode (q, ν) to the total thermal conductivity can be expressed as where Cph(q, ν), vg(q, ν) and τ(q, ν) are volumetric specific heat, group velocity, and lifetime of the phonon mode (q, ν) (q and ν denote the phonon wavevector and the index of phonon branch, respectively), respectively; and N is the total number of q points. Considering the fact that the acoustic phonon modes are usually major energy carriers in thermal transport, the reduced group velocities of acoustic phonon modes in CNT (2, 1) will remarkably reduce its thermal conductivity.

Bottom Line: Detailed lattice dynamic calculations suggest that the acoustic phonon modes greatly soften in CNT (2, 1) as compared to regular CNTs.Moreover, both phonon group velocities and phonon lifetimes strikingly decrease in CNT (2, 1), which result in the remarkable reduction of thermal conductivity.Besides, isotope doping and chemical functionalization enable the further reduction of thermal conductivity in CNT (2, 1).

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Centre for Computational Science and Engineering, and Graphene Research Center, National University of Singapore, Singapore 117542, Republic of Singapore.

ABSTRACT
Molecular dynamic simulations reveal that the ultrathin carbon nanotube (CNT) (2, 1) with a reconstructed structure exhibits a surprisingly low thermal conductivity, which is only ~16-30% of those in regular CNTs, e.g. CNT (2, 2) and (5, 5). Detailed lattice dynamic calculations suggest that the acoustic phonon modes greatly soften in CNT (2, 1) as compared to regular CNTs. Moreover, both phonon group velocities and phonon lifetimes strikingly decrease in CNT (2, 1), which result in the remarkable reduction of thermal conductivity. Besides, isotope doping and chemical functionalization enable the further reduction of thermal conductivity in CNT (2, 1).

No MeSH data available.


Related in: MedlinePlus