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Stable 1T Tungsten Disulfide Monolayer and Its Junctions: Growth and Atomic Structures

Author(s):

Yung-Chang Lin, Chao-Hui Yeh, Ho-Chun Lin, Ming-Deng Siao, Zheng Liu, Hideaki Nakajima, Toshiya Okazaki, Mei-Yin Chou, Kazu Suenaga, Po-Wen Chiu

Journal:

ACS Nano

Year:

2018

Volume:

12

Pages

12080-12088

DOI:

10.1021/acsnano.8b04979

Abstract:

Transition-metal dichalcogenides in the 1T
phase have been a subject of increasing interest, which is
partly due to their fascinating physical properties and partly
to their potential applications in the next generation of
electronic devices, including supercapacitors, electrocatalytic
hydrogen evolution, and phase-transition memories. The
primary method for obtaining 1T WS2 or MoS2 has been
using ion intercalation in combination with solution-based
exfoliation. The resulting flakes are small in size and tend to
aggregate upon deposition, forming an intercalant−TMD
complex with small 1T and 1T′ patches embedded in the 2H
matrix. Existing growth methods have, however, produced
WS2 or MoS2 solely in the 2H phase. Here, we have refined the growth approach to obtain monolayer 1T WS2 up to 80 μm
in size based on chemical vapor deposition. With the aid of synergistic catalysts (iron oxide and sodium chloride), 1T WS2
can nucleate in the infant stage of the growth, forming special butterfly-like single crystals with the 1T phase in one wing
and the 2H phase in the other. Distinctive types of phase boundaries are discovered at the 1T−2H interface. The 1T
structure thus grown is thermodynamically stable over time and even persists at a high temperature above 800 °C,
allowing for a stepwise edge epitaxy of lateral 1T heterostructures. Atomic images show that the 1T WS2−MoS2
heterojunction features a coherent and defectless interface with a sharp atomic transition. The stable 1T phase represents
a missing piece of the puzzle in the research of atomic thin van der Waals crystals, and our growth approach provides an
accessible way of filling this gap.

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