Atomic‐Scale Fabrication of In‐Plane Heterojunctions of Few‐Layer MoS₂ via In Situ Scanning Transmission Electron Microscopy

Abstract

Transition metal dichalcogenides (TMDs) have emerged as promising 2D materials that can be atomically thin semiconductors, semimetals, metals, or even superconductors. These materials consist of transition metal atoms sandwiched between two layers of chalcogen atoms. Their innate layered structure stems from the existence of strong intralayer bonding forces and weak interlayer van der Waals interactions. [1] Recently, studies have uncovered a Layered MoS 2 is a prospective candidate for use in energy harvesting, valleytronics, and nanoelectronics. Its properties strongly related to its stacking configuration and the number of layers. Due to its atomically thin nature, understanding the atomic-level and structural modifications of 2D transition metal dichalcogenides is still underdeveloped, particularly the spatial control and selective precision. Therefore, the development of nanofabrication techniques is essential. Here, an atomic-scale approach used to sculpt 2D few-layer MoS 2 into lateral heterojunctions via in situ scanning/transmission electron microscopy (STEM/TEM) is developed. The dynamic evolution is tracked using ultrafast and high-resolution filming equipment. The assembly behaviors inherent to few-layer 2D-materials are observed during the process and included the following: scrolling, folding, etching, and restructuring. Atomic resolution STEM is employed to identify the layer variation and stacking sequence for this new 2D-architecture. Subsequent energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy analyses are performed to corroborate the elemental distribution. This sculpting technique that is established allows for the formation of sub-10 nm features, produces diverse nanostructures, and preserves the crystallinity of the material. The lateral heterointerfaces created in this study also pave the way for the design of quantumrelevant geometries, flexible optoelectronics, and energy storage devices.

Direct visualization of out-of-equilibrium structural transformations in atomically thin chalcogenides

“…However, with the rapid growth of interest in the optical, electronic, and mechanical properties of TMDCs [17,18], several studies have used in situ scanning transmission electron microscopy (STEM) to document structural transformations under equilibrium conditions [4,[19][20][21]. In addition, some observations of in-situ heterojunction formation and growth have also been made in the same class of materials [22,23]. These nanoscopic investigations have shown that defects and vacancies form due to the application of multiple types of external stimuli, along with the dynamic migration of transition metal and chalcogen atoms towards favourable grain boundary formations [24].…”

Atomic-scale characterization of structural heterogeny in 2D TMD layers

“…8(b–e)). 72 With electron beam MoS 2 layer-thinning, a heterointerface between monolayer and few-layer 2D MoS 2 is demonstrated via dark-field STEM (Fig. 8(b)) as manifested by different Moiré patterns.…”

Growth Mechanism of Periodic-Structured MoS2 by Transmission Electron Microscopy

“…Given that the location of CVD growth of single-layer MoS 2 is relatively random, understanding its growth mechanism can substantially benefit research on MoS 2 growth. TEM helps elucidate the atomic structure and the chemical composition information of particle evolution during catalysis [34][35][36][37][38][39][40]. The material properties of MoS 2 are preferably a single layer or very few layers.…”