Gamma Radiation-Induced Oxidation, Doping, and Etching of Two-Dimensional MoS2 Crystals.

Liam H Isherwood,Ben F Spencer,Cinzia Casiraghi,Aliaksandr Baidak,Gursharanpreet Athwal

doi:10.1021/acs.jpcc.0c10095

Abstract

Two-dimensional (2D) MoS2 is a promising material for future electronic and optoelectronic applications. 2D MoS2 devices have been shown to perform reliably under irradiation conditions relevant for a low Earth orbit. However, a systematic investigation of the stability of 2D MoS2 crystals under high-dose gamma irradiation is still missing. In this work, absorbed doses of up to 1000 kGy are administered to 2D MoS2. Radiation damage is monitored via optical microscopy and Raman, photoluminescence, and X-ray photoelectron spectroscopy techniques. After irradiation with 500 kGy dose, p-doping of the monolayer MoS2 is observed and attributed to the adsorption of O2 onto created vacancies. Extensive oxidation of the MoS2 crystal is attributed to reactions involving the products of adsorbate radiolysis. Edge-selective radiolytic etching of the uppermost layer in 2D MoS2 is attributed to the high reactivity of active edge sites. After irradiation with 1000 kGy, the monolayer MoS2 crystals appear to be completely etched. This holistic study reveals the previously unreported effects of high-dose gamma irradiation on the physical and chemical properties of 2D MoS2. Consequently, it demonstrates that radiation shielding, adsorbate concentrations, and required device lifetimes must be carefully considered, if devices incorporating 2D MoS2 are intended for use in high-dose radiation environments.

Highlights

Nuclear and space applications are the primary fields that could experience a technological step change due to the implementation of light-weight materials and devices with enhanced capabilities, offered by two-dimensional (2D)materials such as transition metal dichalcogenides (TMDCs).the successful deployment of 2D TMDCs in such applications can only be achieved if these materials are resilient and durable upon exposure to high doses of ionizing radiation.[1]
We investigated two types of samples: MoS2 flakes produced by micromechanical exfoliation (MME), which contain a mixture of mono- (1 L), bi- (2 L), tri- (3 L), quadri-layer (4 L), and bulk single crystals, as identified by Raman spectroscopy;[40] and commercially available polycrystalline 1 L films, produced by chemical vapor deposition (CVD)
The thickness of 1 L, 2 L, and 3 L MoS2 crystals can be determined unambiguously by calculating the frequency difference between the A1g and E21g modes using a well-established procedure based on Raman spectroscopy.[40]

Summary

Introduction

Materials such as transition metal dichalcogenides (TMDCs). The successful deployment of 2D TMDCs in such applications can only be achieved if these materials are resilient and durable upon exposure to high doses of ionizing radiation.[1] Our work addresses this important question by investigating the gamma-radiation-induced processes in MoS2 crystals within the high-dose regime under ambient conditions. M = Mo or W and X = S or Se, are semiconductors whose band gaps progressively increase as the crystal thickness is reduced; an indirect−direct transition is observed in monolayer (1 L) crystals.[4,5] In particular, 1 L MoS2 possesses a 1.9 eV direct band gap,[6] which makes it a promising candidate for photovoltaic applications.[7−9] With regard to electronic applications, field-effect transistors incorporating 2D. The atomically thin nature and high electron mobility[10] of 2D

Methods

Results

Conclusion