Layer-number-dependent work function of MoS2 nanoflakes

We investigated the layer-number-dependent work function of MoS2 nanoflakes by using Kelvin probe force microscopy (KPFM) to measure the surface potential. The work functions of as-prepared 1- to 6-layer MoS2 nanoflakes were 5.15–5.39 eV and increased with increasing layer number. After annealing, the work functions of the nanoflakes decreased to 0.1–0.2 eV due to elimination of absorbed molecules on the surface. However, the work function of the edge region of the annealed flakes was relatively larger than that of the internal region. The charge carrier trapping by adsorbed molecules due to the polarity and the hydrophilicity of MoS2 may cause a reduction in the work function of the annealed flakes compared with that for MoS2 exposed to air. The dependence of the obtained work function of MoS2 nanoflakes on the number of layers is essential to the formation of metal contacts for fabricating future MoS2-based devices.