Probing the Electron States and Metal-Insulator Transition Mechanisms in Atomically Thin MoS2 Based on Vertical Heterostructures

TL;DR

This study uses vertical MoS2 heterostructures to investigate electron states and the mechanisms behind the metal-insulator transition, revealing a percolation-type MIT driven by electron density inhomogeneities.

Contribution

It introduces a novel vertical heterostructure approach to probe electron states and elucidate the MIT mechanism in atomically thin MoS2, providing detailed insights into surface electron excitation and band properties.

Findings

Observation of a percolation-type MIT driven by electron density inhomogeneities.

Ability to access and measure surface electron states over a wide frequency and temperature range.

Determination of thickness-dependent band gap and screening effects in MoS2.

Abstract

The metal-insulator transition (MIT) is one of the remarkable electrical transport properties of atomically thin molybdenum disulphide (MoS2). Although the theory of electron-electron interactions has been used in modeling the MIT phenomena in MoS2, the underlying mechanism and detailed MIT process still remain largely unexplored. Here, we demonstrate that the vertical metal-insulator-semiconductor (MIS) heterostructures built from atomically thin MoS2 (monolayers and multilayers) are ideal capacitor structures for probing the electron states in MoS2. The vertical configuration of MIS heterostructures offers the added advantage of eliminating the influence of large impedance at the band tails and allows the observation of fully excited electron states near the surface of MoS2 over a wide excitation frequency (100 Hz-1 MHz) and temperature range (2 K- 300 K). By combining capacitance and transport measurements, we have observed a percolation-type MIT, driven by density inhomogeneities of electron states, in the vertical heterostructures built from monolayer and multilayer MoS2. In addition, the valence band of thin MoS2 layers and their intrinsic properties such as thickness-dependence screening abilities and band gap widths can be easily accessed and precisely determined through the vertical heterostructures.