Anharmonic phonons in few-layer MoS_2: Raman spectroscopy of ultralow energy compression and shear modes

摘要

Molybdenum disulfide (MoS_2) is a promising material for making two-dimensional crystals and flexible electronic and optoelectronic devices at the nanoscale. MoS_2 flakes can show high mobilities and have even been integrated in nanocircuits. A fundamental requirement for such use is efficient thermal transport. Electronic transport generates heat which needs to be evacuated, more crucially so in nanostructures. Anharmonic phonon-phonon scattering is the dominant intrinsic limitation to thermal transport in insulators. Here, using appropriate samples, ultralow energy Raman spectroscopy and first-principles calculations, we provide a full experimental and theoretical description of compression and shear modes of few-layer (FL) MoS_2. We demonstrate that the compression modes are strongly anharmonic with a marked enhancement of phonon-phonon scattering as the number of layers is reduced, most likely a general feature of nanolayered materials with weak interlayer coupling.