Q. Fu, J. Yang*, Y. Chen, D. Li, and D. Xu*, Appl. Phys. Lett. 106, Art. No. 031905 (2015).
We report on experimental studies of the average phonon mean free path in the c-axis direction of graphite. Through systematically measuring the cross-plane thermal conductivity of thin graphite flakes with thickness ranging from 24 nm to 714 nm via a differential three omega method, we demonstrate that the average phonon mean free path in the c-axis direction of graphite is around 200 nm at room temperature, much larger than the commonly believed value of just a few nanometers. This study provides direct experimental evidence for the recently projected very long phonon mean free path along the c-axis of graphite.