Suppressed thermal conductivity in fluorinated diamane: Optical phonon dominant thermal transport

Since surface functionalization can profoundly tune the physical and chemical properties of materials, we performed a comparative study on the thermal conductivities of fluorinated diamane (FD) and compared them with the hydrogenated diamane (HD) to examine the influence of functional groups on the thermal transport properties of diamane. Our results reveal a significant impact of a functional group on the thermal conductivity of diamane. The FD shows an 82% reduced thermal conductivity as compared with the HD. Most strikingly, the dominant phonon modes in thermal transport switches from out-of-plane acoustic (ZA) modes in HD to optical modes in FD. Those results can be understood by the heavy atomic mass of fluorine as opposed to the light hydrogen, which leads to remarkably softened phonon dispersion and the entanglement of optical modes with the acoustic modes. These two factors result in reduced group velocities and enhanced phonon scattering in FD, both of which account for the significantly dropped thermal conductivity of FD. Hence, the mass of functional groups could be employed to tune the thermal transport behavior of 2D materials effectively.