Thickness-dependent Electronic Transport in MoS₂ and WS₂ Two-dimensional Nanostructures
Wei-Chu Shen (沈韋竹)1, Ruei-San Chen (陳瑞山)2*, Ying-Sheng Huang (黃鶯聲)1
1Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan
2Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei 10607, Taiwan
* presenting author:Ruei-San Chen,
Thickness-dependent electronic transport properties in the molybdenum disulphide (MoS2) and the tungsten disulphide (WS2) two-dimensional (2D) nanostructures beyond quantum confinement scale were observed and investigated. It is found that the nanoflakes produced by simple mechanical exfoliation exhibit several orders of magnitude higher conductivity than their bulk counterparts. The smaller activation energies of carrier were also observed for the MoS2 and WS2 nanoflakes in comparison to the bulk counterparts. These results imply the presence of higher surface conductivity or electron surface accumulation in the layer semiconductor systems. In addition, the potential artificial effects, that could result in a high electron density at the surface, including electron injection from the substrate and surface damage by ion bombardment, were excluded. This result further indicates the proposed surface electron accumulation is an inherent characteristic, which might be generally applicable to the transition metal dichalcogenide (TMD) layer semiconductors. The finding provides a probable explanation to the consistent observations of anomalously high conductive nature in the TMD 2D layer materials and is also crucial for development of next-generation ultrathin, flexible and transparent electronics and optoelectronics.

Keywords: molybdenum disulphide , tungsten disulphide, nanostructure, conductivity