Platinum diselenide (PtSe2) is an emerging class of two-dimensional (2D) transition-metal dichalcogenide (TMD) crystals recently gaining substantial interest, owing to its extraordinary properties absent in conventional 2D TMD layers. Most interestingly, it exhibits a thickness-dependent semiconducting-to-metallic transition, i.e., thick 2D PtSe2 layers, which are intrinsically metallic, become semiconducting with their thickness reduced below a certain point. Realizing both semiconducting and metallic phases within identical 2D PtSe2 layers in a spatially well-controlled manner offers unprecedented opportunities toward atomically thin tailored electronic junctions, unattainable with conventional materials. In this study, beyond this thickness-dependent intrinsic semiconducting-to-metallic transition of 2D PtSe2 layers, we demonstrate that controlled plasma irradiation can "externally" achieve such tunable carrier transports. We grew wafer-scale very thin (a few nm) 2D PtSe2 layers by a chemical vapor deposition (CVD) method and confirmed their intrinsic semiconducting properties. We then irradiated the material with argon (Ar) plasma, which was intended to make it more semiconducting by thickness reduction. Surprisingly, we discovered a reversed transition of semiconducting to metallic, which is opposite to the prediction concerning their intrinsic thickness-dependent carrier transports. Through extensive structural and chemical characterization, we identified that the plasma irradiation introduces a large concentration of near-atomic defects and selenium (Se) vacancies in initially stoichiometric 2D PtSe2 layers. Furthermore, we performed density functional theory (DFT) calculations and clarified that the band-gap energy of such defective 2D PtSe2 layers gradually decreases with increasing defect concentration and dimensions, accompanying a large number of midgap energy states. This corroborative experimental and theoretical study decisively verifies the fundamental mechanism for this externally controlled semiconducting-to-metallic transition in large-area CVD-grown 2D PtSe2 layers, greatly broadening their versatility for futuristic electronics.
Bibliographical noteFunding Information:
Y.J. acknowledges financial support from the National Science Foundation (CMMI-1728390) (M.S.S. and Y.J.), the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No. 20173010013340), and the VPR Advancement of Early Career Researchers award from the University of Central Florida. This research was in part supported by the Creative Materials Discovery Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (NRF-2017M3D1A1039553). The work at SNU was supported by the National Research Foundation of Korea (NRF-2018R1D1A1B07043973, 2017R1A5A1014862, SRC program: vdWMRC center) and Creative-Pioneering Researchers Program through Seoul National University (SNU). H.S.C. was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2019R1F1A1058410).
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All Science Journal Classification (ASJC) codes
- Materials Science(all)