High conduction hopping behavior induced in transition metal dichalcogenides by percolating defect networks: toward atomically thin circuits

TL;DR

This study demonstrates how focused helium ion irradiation induces defect networks in monolayer transition metal dichalcogenides, enabling tunable hopping conduction and the creation of atomically thin electronic circuits with high performance.

Contribution

It introduces a method to induce pseudo-metallic behavior and percolating defect networks in WSe$_2$ and WS$_2$ using focused He$^+$ irradiation, enabling atomically thin circuit fabrication.

Findings

Induced pseudo-metallic behavior in WSe$_2$ and WS$_2$ via He$^+$ irradiation.

Formation of percolating defect networks at a critical dose.

Successful fabrication of atomically thin resistor and transistor circuits.

Abstract

Atomically thin circuits have recently been explored for applications in next-generation electronics and optoelectronics and have been demonstrated with two-dimensional lateral heterojunctions. In order to form true 2D circuitry from a single material, electronic properties must be spatially tunable. Here, we report tunable transport behavior which was introduced into single layer tungsten diselenide and tungsten disulfide by focused He$^+$ irradiation. Pseudo-metallic behavior was induced by irradiating the materials with a dose of ~1x10$^{16} He^+/cm^2$ to introduce defect states, and subsequent temperature-dependent transport measurements suggest a nearest neighbor hopping mechanism is operative. Scanning transmission electron microscopy and electron energy loss spectroscopy reveal that Se is sputtered preferentially, and extended percolating networks of edge states form within WSe$_2$ at a critical dose of 1x10$^{16} He^+/cm^2$. First-principles calculations confirm the semiconductor-to-metallic transition of WSe$_2$ after pore and edge defects were introduced by He$^+$ irradiation. The hopping conduction was utilized to direct-write resistor loaded logic circuits in WSe$_2$ and WS$_2$ with a voltage gain of greater than 5. Edge contacted thin film transistors were also fabricated with a high on/off ratio (> 10$^6$), demonstrating potential for the formation of atomically thin circuits.