Phonon transport in graphene elucidated using isotopic heterointerfaces
Takayuki Arie, Osaka Prefecture University
Since phonons are the main heat carrier in carbon nanomaterials, we have been investigating the change in heat transport in the materials by introducing isotopes  and defects . Phonon transport is also inhibited by domain boundaries; therefore, we investigate the effect of isotopic heterointerfaces on phonon transport properties in graphene.
Heterostructures of graphene composed of 12C and 13C can be synthesized in single crystalline graphene by continuously switching the source gases during chemical vapor deposition process. Raman spectral mapping from single-crystal graphene shows that each graphene has Raman peaks corresponding to 12C-graphene or 13C-graphene, indicating that the heterointerfaces were repeatedly fabricated. The apparent thermal resistance of the devices with respect to the interface number indicates that the resistance increases linearly as the interface number less than 4. The interfacial thermal resistance was estimated as 125 μm2K/W. In the device with 4 interfaces, however, the resistance increases more significantly. As the distance between interfaces is approximately 600 nm in this device, which is shorter than the reported mean free path of phonon in graphene at room temperature, the heat transport in the device more likely changes from diffusive to quasi-ballistic regime, leading to a dramatic increase in the interfacial thermal resistance. Y. Anno, K. Takei, S. Akita, and T. Arie, Phys. Status Solidi RRL 8, 692 (2014).
 Y. Anno, Y. Imakita, K. Takei, S. Akita, and T. Arie, 2D Mater. 4, 025019 (2017).
Figure (a) Optical image of single-crystal graphene grown by chemical vapor deposition. (Inset) Raman spectral mapping of 2D band intensities.
Figure (b) Thermal resistance change with respect to the interface number in the device.