Through integrated molecular dynamics simulations and experimental studies, the feasibility of an ion-irradiation plus annealing based phonon engineering technique to enhance the thermal conductivity of carbon nanotube films was demonstrated. Upon ion irradiation of carbon nanotube films, both inter-tube defects and intra-tube defects were introduced. The molecular dynamics simulations showed that inter-tube defects created between neighboring tubes were much more stable than were intra-tube defects created on tube graphitic planes. Upon thermal annealing, intra-tube defects were preferentially removed but inter-tube defects remained. Consequently, axial phonon transport increased due to reduced phonon scattering and off-axial phonon transport was sustained due to the high stability of inter-tube defects, leading to a conductivity enhancement upon annealing. The modeling predictions agreed with experimental observations that thermal conductivities of carbon nanotube films were enhanced after 2MeV hydrogen ion irradiation and the conductivities were further enhanced upon post irradiation annealing.

Introducing Thermally Stable Inter-Tube Defects to Assist Off-Axial Phonon Transport in Carbon Nanotube Films. J.Wang, D.Chen, J.Wallace, J.Gigax, X.Wang, L.Shao: Applied Physics Letters, 2014, 104[19], 191902