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Small. 2017 Jan;13(1). doi: 10.1002/smll.201601930. Epub 2016 Oct 17.

Chain Vacancies in 2D Crystals.

Zhao J1,2, Nam H1,3, Ly TH1,2, Yun SJ1,2, Kim S2, Cho S1,2, Yang H2, Lee YH1,2,3.

Author information

1
Center for Integrated Nanostructure Physics (CINAP), Institute for Basic Science (IBS), Sungkyunkwan University, Suwon, 440-746, South Korea.
2
Department of Energy Science, Sungkyunkwan University, Suwon, 440-746, South Korea.
3
Department of Physics, Sungkyunkwan University, Suwon, 440-746, South Korea.

Abstract

Defects in bulk crystals can be classified into vacancies, interstitials, grain boundaries, stacking faults, dislocations, and so forth. In particular, the vacancy in semiconductors is a primary defect that governs electrical transport. Concentration of vacancies depends mainly on the growth conditions. Individual vacancies instead of aggregated vacancies are usually energetically more favorable at room temperature because of the entropy contribution. This phenomenon is not guaranteed in van der Waals 2D materials due to the reduced dimensionality (reduced entropy). Here, it is reported that the 1D connected/aggregated vacancies are energetically stable at room temperature. Transmission electron microscopy observations demonstrate the preferential alignment direction of the vacancy chains varies in different 2D crystals: MoS2 and WS2 prefer 〈2¯11〉 direction, while MoTe2 prefers 〈1¯10〉 direction. This difference is mainly caused by the different strain effect near the chalcogen vacancies. Black phosphorous also exhibits directional double-chain vacancies along 〈01〉 direction. Density functional theory calculations predict that the chain vacancies act as extended gap (conductive) states. The observation of the chain vacancies in 2D crystals directly explains the origin of n-type behavior in MoTe2 devices in recent experiments and offers new opportunities for electronic structure engineering with various 2D materials.

KEYWORDS:

ab initio; black phosphorous; transition metal dichalcogenide; transmission electron microscopy; vacancy defects

PMID:
27748996
DOI:
10.1002/smll.201601930

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