Raman spectroscopy of the interlayer shear mode in few-layer MoS2 flakes
  Single- and few-layer MoS2 has recently gained attention as an interesting new material system for opto-electronics. Here, we report on scanning Raman measurements on few-layer MoS2 flakes prepared by exfoliation. We observe a Raman mode corresponding to a rigid shearing oscillation of adjacent layers. This mode appears at very low Raman shifts between 20 and 30 relative wavenumbers. Its position strongly depends on the number of layers, which we independently determine using AFM measurements and investigation of the other characteristic Raman modes. Raman spectroscopy of the shear mode therefore is a useful tool to determine the number of layers for few-layer MoS2 flakes. 
G. Plechinger, S. Heydrich, J. Eroms, D. Weiss, Sch\"uller, and T.   Korn
cond-mat.mtrl-sci cond-mat.mes-hall