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Prof. Young Hee LEE, Center for Integrated Nanostructure Physics, Institute for Basic Science at Sungkyunkwan University has successfully developed a new method for converting monolayer molybdenum disulfide (MoS2) into molybdenum ditelluride (MoTe2) via substitution of tellurium to MoS2 by chemical vapor deposition (CVD).
In order to trigger such a substitutional reaction, High reaction temperature is necessary for Te-substitution but the instability arises because of lower thermal stability of MoTe2 than that of MoS2. Although the MoTe2, which is product after Te-substitution, is vaporized above 700 °C due to the thermal instability, the substitutional reaction below 700 °C is no longer possible. To resolve this issue, we introduced sodium telluride (Na2Te) as a telluriding catalyst and further was able to achieve stable MoTe2 by provoking substitutional reaction at temperature below 700 °C.
The research team confirmed that the Te-substitution reaction occurs preferentially from the edge and grain boundary of the MoS2 flake and further constructed lateral hetero semiconductor junction of MoS2-MoTe2. Furthermore, various phases such as alloy (MoS2-xTex), semiconductor (2H-MoTe2), and metal (1T’-MoTe2) were obtained by adjusting experimental parameters of temperature and sodium concentration. We also demonstrated that the band gap of MoS2-xTex alloy can be modulated by controlling the tellurium composition.
Dr. Seok Jun YUN, the leading scientist of the research team, predicted that "It is possible to synthesize compound materials by a substitutional technique even for the unstable compounds."
The conversion method using the telluriding catalyst (Na2Te) can be applied not only to MoS2 but also to tungsten disulfide (WS2), which is another type of transition metal dichalcogenide.
This research, conducted by prof. Young Hee Lee and Seok Joon Yun who is the first author of this research, was published in Nature Communications (IF 12.124), a worldwide scientific journal in science and technology, on December 18.
[Figure 1] The conversion process of monolayer molybdenum disulfide to molybdenum ditelluride
[Figure 2] The phase modulation diagram with sodium hydroxide concentration and telluriding temperature
[Figure 2] The phase modulation diagram with sodium hydroxide concentration and telluriding temperature
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