Mechanical and Kelvin Probe Force Microscopy Investigations of Ultrathin Membranes Based on MoS₂ and MoSe₂

Herein, three atomically thin membranes based on MoS2, MoSe2, and MoS1.44Se0.56 alloy are studied by atomic force microscopy (AFM). The mechanical and electrical properties of the alloy are compared to MoS2 and MoSe2. Based on the contact potential difference values obtained from AFM measurements with a Kelvin probe, the work function of the layers is determined to be 4.63 +/- 0.08, 5.10 +/- 0.09, and 5.17 +/- 0.11 eV, for suspended MoS2, MoSe2, and MoS1.44Se0.56, respectively. In addition, a noticeable difference (approximate to 0.02 eV) between the work function of supported and suspended areas is observed. The elastic deformation of the freely suspended layers is studied by nanoindentation using AFM. This allows the determination of Young's modulus values, which are 247.96 +/- 1.8, 127.60, and 101.23 GPa for MoS2, MoSe2, and MoS1.44Se0.56, respectively. From this study, it is concluded that both the work function and Young's modulus of MoS1.44Se0.56 alloy do not interpolate linearly between MoS2 and MoSe2.