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

Herein, three atomically thin membranes based on MoS 2 , MoSe 2 , and MoS 1.44 Se 0.56 alloy are studied by atomic force microscopy (AFM). The mechanical and electrical properties of the alloy are compared to MoS 2 and MoSe 2 . 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 MoS 2 , MoSe 2 , and MoS 1.44 Se 0.56 , respectively. In addition, a noticeable difference (≈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 MoS 2 , MoSe 2 , and MoS 1.44 Se 0.56 , respectively. From this study, it is concluded that both the work function and Young's modulus of MoS 1.44 Se 0.56 alloy do not interpolate linearly between MoS 2 and MoSe 2 .