Suyeon Cho

Affiliation: Division of Chemical Engineering and Materials Science, Ewha Womans University

Date: January 27, 2021; 15:00 – 16:00

Phase engineering in MoTe2

Two-dimensional atomic crystals such as transition metal dichalcogenides (TMDs) have recently attracted renewed interests for the important components of next-generation nanoelectronic devices. Most studies have focused on the semiconducting hexagonal 2H phases of TMDs. Other phases such as monoclinic 1T or 1T’ have not been studied well because it has been believed that those phases are thermodynamically unstable. However, two different phases, semiconducting hexagonal (2H) and metallic monoclinic (1T’), have been successfully synthesized as high quality single crystals in one of TMDs, MoTe2by the control of synthetic temperature. It is found that the electronic phase transition between semi-metallic (bulk) and semiconducting (few-layered) appears in newly found monoclinic 1T’-MoTe2. The phase engineering between semiconducting 2H and metallic 1T’ phase of MoTe2 can be achieved by laser-irradiation which produces Te vacancy on the surface of MoTe2. In-situ scanning transmission electron microscopy results combined with theoretical calculations reveal that the Te vacancy triggers the local phase transition in MoTe2. We performed the phase patterning on MoTe2 surface using the laser irradiation with 200 nm-sized spot. The insertion of a metallic 1T’- MoTe2 layer into the interface of an Au electrode and a semiconducting2H-MoTe2 film results a true 2D device, converting a schottky contact to an ohmic contact with large carrier mobility and a high on/off current ratio of 106.

Reference:
1. Suyeon Cho, S. Kim, J. H. Kim, J.Zhao, J. Seok, D. H. Keum, J. Baik, D.-H. Choe, K. J. Chang, K. Suenaga, S. W.Kim, Y. H. Lee, H. Yang, “PhasePatterning for Ohmic Homojunction Contact in MoTe2”, Science, 349(6248), 625 (2015)
2. D. H. Keum†, Suyeon Cho†, J. H. Kim, D.-H.Choe, H.-J. Sung, M. Kan, H. Kang, J.-Y. Hwang, S. W. Kim, H. Yang, K. J. Chang, Y. H. Lee, “Bandgapopening in few-layered monoclinic MoTe2”, Nature Physics, 11, 482-486 (2015)