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Understanding Substrate-Guided Assembly in van der Waals Epitaxy by in Situ Laser Crystallization within a
Chenze Liu1, Yu-Chuan Lin1, Mina Yoon1
1Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States.
ACS Nano
|April 30, 2021
Summary
Researchers used in situ laser heating in a transmission electron microscope (TEM) to observe the growth of two-dimensional (2D) heterostructures. This method reveals how pulsed laser deposition (PLD) and substrate templating guide the formation of van der Waals (vdW) epitaxial layers.
Area of Science:
- Materials Science
- Nanotechnology
- Surface Science
Background:
- Atomically thin two-dimensional (2D) crystals and heterostructures are crucial for advanced electronic and optoelectronic devices.
- Developing scalable and precise synthesis methods for 2D heterostructures with tailored properties is an ongoing challenge.
Purpose of the Study:
- To investigate the bottom-up synthesis mechanisms of 2D van der Waals (vdW) epitaxial heterostructures.
- To understand the crystallization and coalescence dynamics of amorphous precursors on 2D crystalline substrates using in situ TEM.
- To explore the role of substrate lattice matching in guiding the growth of high-quality 2D heterostructures.
Main Methods:
- Utilized in situ laser heating within a transmission electron microscope (TEM).
- Deposited amorphous tungsten selenide (WSe2) precursors using pulsed laser deposition (PLD) onto graphene and molybdenum diselenide (MoSe2) monolayer substrates.
- Applied stepwise laser heating treatments to induce crystallization and coalescence.
- Performed first-principles calculations to understand substrate-induced energetics.
Main Results:
- Observed the stepwise evolution of amorphous precursors into 2D heterostructures under laser heating.
- Demonstrated that MoSe2 substrate lattice matching guides the formation of large-domain, heteroepitaxial vdW WSe2/MoSe2 bilayers.
- Identified nonclassical particle attachment processes, including domain rotation and grain boundary migration, assisting coalescence.
- Confirmed favorable energetics for domain rotation due to lattice matching via calculations.
Conclusions:
- In situ TEM laser heating is a powerful tool for studying nonequilibrium crystallization and exploring synthesis pathways for 2D materials.
- Substrate-guided crystallization and coalescence are critical for achieving high-quality vdW epitaxial heterostructures.
- Understanding these growth mechanisms provides insights into the pulsed laser deposition (PLD) and laser crystallization of 2D materials.
