Anomalous thermal anisotropy of two-dimensional nanoplates of vertically grown MoS2

Heat flow control plays a significant role in thermal management and energy conversion processes. Recently, two dimensional (2D) materials with unique anisotropic thermal properties are attracting a lot of attention, as promising building blocks for molding the heat flow. Originated from its crystal structure, in most if not all the 2D materials, the thermal conductivity along the Z direction (kz ) is much lower than x-y plane thermal conductivity (kxy ). In this work, we demonstrate that 2D nanoplates of vertically grown molybdenum disulfide (VG MoS2) can have anomalous thermal anisotropy, in which kxy (about 0.83 W/m K at 300 K) is ∼1 order of magnitude lower than kz (about 9.2 W/m K at 300 K). Lattice dynamics analysis reveals that this anomalous thermal anisotropy can be attributed to the anisotropic phonon dispersion relations and the anisotropic phonon group velocities along different directions. The low kxy can be attributed to the weak phonon coupling near the x-y plane interfaces. It is expected that this 2D nanoplates of VG MoS2 with anomalous thermal anisotropy and low kxy can serve as a complementary building block for device designs and advanced heat flow control.