Step‐By‐Step Atomic Insights into Structural Reordering from 2D to 3D MoS₂

Abstract

Vertically stacked low‐dimensional heterostructures are outstanding systems both for exploring fundamental physics and creating new devices. Due to nanometer‐scale building blocks, atomic scale phenomena become for them of fundamental importance, including during device operation. These can be accessed in situ in aberration‐corrected scanning transmission electron microscopy (STEM) experiments. Here, the dynamics of a graphene‐MoS2 heterostructure are studied under Joule heating, where the graphene serves as a high temperature atomically thin and electron transparent “hot plate” for the MoS2. Structural dynamics and evolution of the system are shown at the atomic scale, demonstrating that at the highest temperatures (estimated to exceed 2000 K), the continuous 2D MoS2 transforms into separated 3D nanocrystals, initiated by sulfur vacancy creation and migration followed by formation of voids and clustering at their edges. The resulting nanocrystals exhibit predominantly hexagonal shapes with the 2H and hybrid (2H/3R, 3R/TZ) polytypes. The observed morphology of the crystals is further discussed during and after the transformation, as well as their different edge configurations and stability under electron irradiation. These observations of MoS2 at extreme temperatures provide insights into the operation of devices based on graphene/MoS2 heterostructures and ultimately may help device fabrication techniques to create MoS2‐based nanostructures, for example, in hydrogen evolution reaction applications.

In Situ Liquid Cell Transmission Electron Microscopy Study of Studtite Particle Formation and Growth via Electron Beam Radiolysis

“…Controlling particle morphology is of great importance to many industries including semiconductors, nanomaterials, and steel fabrication. − Levlev et al showed that a mechanistic understanding of nucleation and growth mechanisms can lead to improved modeling of material properties and future material discovery . In the nuclear industry, particle morphology can impact the environmental transport of uranium, nuclear fuel performance in reactors, long-term storage of spent nuclear fuel, and support nuclear forensics and nuclear safeguards in identifying the processing history of nuclear materials. ,, Prior studies have identified many variables including pH, temperature, reaction time, and calcination temperature that impact the final particle morphology. − Advancements in particle segmentation and machine learning enable quantification of even subtle morphology changes. , The challenge, however, has been in understanding the fundamental principles that result in unique particle morphologies based on the chemical and physical processing conditions.…”

Peeling off the surface: Pt‐decoration of WSe2 nanoflakes results in exceptional photoelectrochemical HER activity

“…22,23 The first paper on inter-layer vacancy migration appeared in 2014 for multilayer graphene. 24 In the case of TMDCs, both theoretical and experimental evidence have been presented recently to show heat-induced migration of S-, 25 or Se-vacancies 26 in the respective metal chalcogenides. Regarding other semiconductors, a defect migration process was reported for TiO 2 , where the number of surface oxygen vacancies increased on Pt-decorated TiO 2 by migration of bulk vacancies to the surface.…”

In Situ Atomic‐Scale Observation of Monolayer MoS2 Devices under High‐Voltage Biasing via Transmission Electron Microscopy

“…[37][38][39] For in situ biasing of 2D materials, relevant research is hardly found in the literature. [40][41][42][43][44] Herein, we focus on the structural evolution of a suspended MoS 2 device under high bias conditions through an advanced in situ technique. Fan et al have studied the electrical breakdown of tungsten disulfide (WS 2 ), and examined the results of mono-and fewlayer samples.…”

“…[43] Inani et al have fabricated the graphene/MoS 2 heterostructure and investigated its dynamic behavior induced by Joule heating, which takes place mainly in graphene, then transfers some of the heat to the MoS 2 similar to a hot plate. [44] In this work, we expect to verify the effect of bias on the material damage by investigating the in situ results at different voltages and the ex situ results. With the help of microelectromechanical system (MEMS) technology, we are able to create a lab-on-achip biasing environment for real-time observation.…”