▎ 摘　　要

This work reports on the phonon energy inversion in graphene nanoribbons: after initial localized thermal excitation, the energy of initial cold phonons (flexural mode: FM) becomes higher than that of local hot phonons (longitudinal and transverse modes: LM/TM). Such energy inversion holds for about 50 picoseconds. Two physical factors combine together to give rise of this phenomenon: one is the much faster heat conduction by FM phonons than that by LM/TM phonons, and the other factor is the strongly temperature-dependent energy exchange rate between FM and LM/TM phonons: 3.7 x 10(10) s(-1) at 84 K to 20.3 x 10(10) s(-1) at around 510 K. (c) 2013 Elsevier B.V. All rights reserved.