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Thermodynamically stable octahedral MoS2 in van der Waals hetero-bilayers

Ahmed, Tanweer and Naik, Mit H and Kumari, Simran and Suman, Smriti P and Debnath, Rahul and Dutta, Sudipta and Waghmare, Umesh and Jain, Manish and Ghosh, Arindam (2019) Thermodynamically stable octahedral MoS2 in van der Waals hetero-bilayers. In: 2D MATERIALS, 6 (4).

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Official URL: https://dx.doi.org/10.1088/2053-1583/ab2822


Reversible switching of the structural ground state of a solid is a fundamental goal in materials engineering, which has not been achieved in atomically thin layers of van der Waals crystals. This is particularly important for the transition metal dichalcogenides, such as molybdenum disulphide (MoS2), where the higher-energy octahedral polymorphs exhibit a wide range of fascinating properties. Here we show that thermodynamically stable octahedral phase of monolayer MoS2 can be achieved in coexistence with the 1H phase, at temperatures below similar to 500 K, by forming a van der Waals hybrid with another layered solid, such as hexagonal boron nitride (hBN) or graphene. Spatial mapping and temperature-dependence of the zone-folded Raman modes reveal that the octahedral phase exists only within the heterostructure region, and exhibits remarkable stability to repeated thermal cycling. A concurrent shift in the out-of-plane A1(g) vibrational mode of MoS2, and near-absence of the octahedral phase in homo-epitaxial structures, suggest likely role of local lattice relaxation due to incommensurability-driven stress fields. Our experiment establishes van der Waals hetero-epitaxy as a new tool for crystal structure engineering in atomic membranes.

Item Type: Journal Article
Publication: 2D MATERIALS
Additional Information: copyright for this article belongs to IOP PUBLISHING LTD
Keywords: Van der Waals heterostructures; transition metal dichalcogenides; 1T ` phase; structural phase transformation; Raman spectroscopy
Department/Centre: Division of Interdisciplinary Sciences > Centre for Nano Science and Engineering
Division of Physical & Mathematical Sciences > Physics
Date Deposited: 05 Sep 2019 06:35
Last Modified: 05 Sep 2019 06:35
URI: http://eprints.iisc.ac.in/id/eprint/63440

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