Control of Radiation Damage in MoS2 by Graphene Encapsulation

Abstract: Recent dramatic progress in studying various two-dimensional (2D) atomic crystals and their heterostructures calls for better and more detailed understanding of their crystallography, reconstruction, stacking order, etc. For this, direct imaging and identification of each and every atom is essential. Transmission Electron Microscopy (TEM) and Scanning Transmission Electron Microscopy (STEM) are ideal, and perhaps the only tools for such studies. However, the electron beam can in some cases induce dramatic structure changes and radiation damage becomes an obstacle in obtaining the desired information in imaging and chemical analysis in the (S)TEM. This is the case of 2D materials such as molybdenum disulfide MoS2, but also of many biological specimens, molecules and proteins. Thus, minimizing damage to the specimen is essential for optimum microscopic analysis. In this letter we demonstrate, on the example of MoS2, that encapsulation of such crystals between two layers of graphene allows for a dramatic improvement in stability of the studied 2D crystal, and permits careful control over the defect nature and formation in it. We present STEM data collected from single layer MoS2 samples prepared for observation in the microscope through three distinct procedures. The fabricated single layer MoS2 samples were either left bare (pristine), placed atop a single-layer of graphene or finally encapsulated between single graphene layers. Their behaviour under the electron beam is carefully compared and we show that the MoS2 sample 'sandwiched' between the graphene layers has the highest durability and lowest defect formation rate compared to the other two samples, for very similar experimental conditions.

• The paper demonstrates that graphene encapsulation of MoS₂ enhances resistance to electron beam damage, preventing defect formation at doses over 1.7×10¹¹ e/Ų.
• The study compares bare, supported, and encapsulated MoS₂, showing that the graphene/MoS₂/graphene structure significantly mitigates radiation-induced damage.
• The findings imply that this encapsulation method can extend to other 2D materials, enabling more accurate structural and chemical analysis under high electron doses.

Control of Radiation Damage in MoS2 by Graphene Encapsulation

The paper presents a comprehensive investigation into the mitigation of radiation damage in molybdenum disulfide (MoS₂) by employing a novel encapsulation technique utilizing single-layer graphene. The study is pivotal for researchers aiming to optimize Imaging and analysis of two-dimensional materials under Transmission Electron Microscopy (TEM) and Scanning Transmission Electron Microscopy (STEM) conditions.

Recent advancements in two-dimensional (2D) materials, including MoS₂, necessitate the development of methods to minimize beam-induced damage during electron microscopy. MoS₂, a notable transition metal dichalcogenide (TMD), is particularly vulnerable to radiation damage mechanisms such as knock-on displacement and ionization. This vulnerability poses challenges in both structural imaging and chemical mapping, inevitably distorting the data obtained from these analyses.

The research explores the effectiveness of three different preparation techniques for MoS₂ samples under electron beam exposure: (1) bare MoS₂, (2) MoS₂ supported on single-layer graphene, and (3) MoS₂ encapsulated between two layers of graphene. The encapsulation protocol demonstrates significantly enhanced durability of MoS₂ under irradiation. Notably, the graphene/MoS₂/graphene structure not only prevents defect formation but also facilitates high-resolution imaging and comprehensive chemical analysis at substantially higher electron doses compared to the pristine and singly supported samples.

Quantitatively, the encapsulated MoS₂ endured doses exceeding 1.7 x 10¹¹ e/Ų without defect formation, a stark improvement over the unencapsulated sample. These results attribute to the superior thermal and electrical conductive properties of graphene, which aid in charge dissipation, effectively minimizing ionization damage. Additionally, the two graphene layers provide a physical barrier that shields the MoS₂ from environmental contaminants and mechanical stress.

The implications of these findings are far-reaching in both theoretical and practical contexts. The presented encapsulation technique is a feasible strategy for extending the lifespan and integrity of other beam-sensitive materials in electron microscopy. This approach opens new avenues for the precise, defect-free exploration of electronic properties in 2D materials, including studies related to their doping, interface dynamics, and potential integration into electronic devices.

Anticipating future research, the study lays the groundwork for exploring interlayer bonding effects between graphene and MoS₂, which could modify electronic interactions and facilitate innovative applications in nanoelectronics. Additionally, the scalability of graphene encapsulation methods could be optimized for a variety of 2D material systems beyond MoS₂, spanning applications in semiconductors, optoelectronic devices, and catalysis.

In conclusion, the use of graphene encapsulation as introduced in this study represents a crucial advancement in TEM and STEM methodologies, enhancing data fidelity and offering a protective platform for radiation-sensitive materials.