Controlling the stacking and conversion in bilayer crystals and heterostructures by non-equilibrium synthesis and processing is very important to construct 2D moiré quantum materials. Here we will show how to introduce isotopes, laser thinning, and Raman spectroscopy to understand the bilayer growth mechanism in two-step chemical vapor deposition. Then we will describe a feedback approach to reveal and control the transformation pathways in bilayer 2D materials by pulsed laser deposition (PLD). We will focus on the transformation kinetics of bilayer WS2 crystals into Janus WSSe/WS2 and WSe2/WS2 heterostructures by hyperthermal implantation of laser-vaporized Se clusters. In situ ICCD imaging, ion probe, and spectroscopy diagnostics characterize the PLD plasma and are used to precisely control the kinetic energies of the Se species arriving at the substrate. In situ Raman spectroscopy is used to characterize the conversion kinetics and capture the metastable phases during transformation. DFT calculations, XPS, and atomic-resolution HAADF STEM are used to identify the compositions, vibrational modes, and structures for revealing the conversion mechanism of the bilayer crystals.
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