Layer number dependent barrier height of MoS₂ on ultra-flat conducting surfaces

Transition metal dichalcogenides (TMDs) are layered semiconducting van der Waal crystals and promising materials for wide range of electronic and optoelectronic devices. Realizing practical device application requires an understanding of nanoscale local electronic and optoelectronic properties on layered TMDs on a conducting metal surface. In this work, we have used conducting atomic force microscopy (CAFM) of layered MoS2 (1-5 layers) immobilized on two different ultra-flat conducting surfaces (RMS surface roughness <0.2 nm) Au and indium tin oxide (ITO) forming metal (conductive-tip)-semiconductor-metal devices. First, we have found that the edges of the different layers are insulating. Second, the current increases as the layer number increases. By applying Fowler-Nordheim tunneling theory, we have determined the barrier heights for different layers and observed that the barrier height decreases as the number of layers increases. Our study provides a fundamental understanding of the local electronic behavior of TMD depending on layer numbers and may pave an avenue toward developing nanoscale electronic devices with tailored properties of different layers.