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[Figure 1] Professor Hyoungsub Kim (AMSE, co-corresponding author), Dr. Eunha Lee (SAIT, co-corresponding author)

The joint research team led by Prof. Hyoungsub Kim (AMSE) and Dr. Eunha Lee (SAIT) first discovered the appearance of highly ordered arrays of 1D intermediate crystals during the chemical transformation of MoO₂ to 2D layer-structured MoS₂.

Recently, for application to next-generation semiconductor and energy devices, numerous researches have been actively conducted to synthesize various 2D layer-structured materials (transition-metal dichalcogenides) via a thermal sulfidation- or selenization-based conversion process of metal oxides. Ideally, such a synthesis process follows sequential layer-by-layer phase transformation characteristics of an atomic layer-level thickness.

During the sulfidation process of MoO₂, the joint research team directly observed the appearance of highly ordered arrays of 1D intermediate crystals at the MoO₂/MoS₂ interface using STEM with an atomic-scale resolution. They also developed a comprehensive structural model and energetics of the intermediate crystals during the dimension-breaking transformation process (3D→1D→2D) based on the first-principles DFT calculations.

[Figure 2] (left) Schematic illustration of chemical phase transformation, (right) STEM images

Furthermore, by collaborating with a Prof. Mann-Ho Cho’s team (department of physics at Yonsei University), they proved possible modulation of the metal-contact type (from p- to n-type) with the number of atomic MoS₂ layers via X-ray photoelectron spectroscopy, which can be used for innovative device applications.

In this paper, Dr. Hyangsook Lee (SAIT) and Dr. Yeonchoo Cho (SAIT) contributed as co-first authors, and the results were published online in ‘Materials Today (Impact Factor = 26.416, JCR Ranking Top 2.7%)' on March 17, 2021.

※ Paper title: “3D-to-2D phase transformation through highly ordered 1D crystals from transition-metal oxides to dichalcogenides”

※ Paper source:  https://www.sciencedirect.com/science/article/abs/pii/S1369702121000560