Journal
ACS NANO
Volume 9, Issue 3, Pages 3274-3283Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsnano.5b00410
Keywords
2D TMD; microstructure; stoichiometry; HRTEM; MBE; CVD; DFT; defects
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Funding
- DFG (German Research Foundation)
- Ministry of Science, Research and the Arts (MWK) of Baden-Wurttemberg
- DFG SPP 1459 Graphene project
- Finnish Cultural Foundation
- Academy of Finland [263416]
- Academy of Finland through its Centres of Excellence Programme [251748]
- Swiss NSF [PP00P2_133552]
- ERC project TopoMat [306504]
- Swiss National Supercomputing Centre (CSCS) [s515]
- ERC grant Flatronics [240076]
- European Research Council (ERC) [240076] Funding Source: European Research Council (ERC)
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We study the atomic scale microstructure of non-stoichiometric two-dimensional(2D) transition metal dichalcogenide MoSe2-x, by employing aberration-corrected high-resolution transmission electron microscopy. We show that a Se-deficit in single layers of MoSe2 grown by molecular beam epitaxy gives rise to a dense network of mirror-twin-boundaries (MTBs) decorating the 2D-grains. With the use of density functional theory calculations, we further demonstrate that MTBs are thermodynamically stable structures in Se-deficient sheets. These line defects host spatially localized states with energies close to the valence band minimum, thus giving rise to enhanced conductance along straight MTBs. However, electronic transport calculations show that-the transmission of hole charge carriers across MTBs is strongly suppressed due to band bending effects. We further observe formation of MTBs during in situ removal of Se atoms by the electron beam of the microscope, thus confirming that MTBs appear due-to Se-deficit, and not coalescence of individual grains during growth. At a very high local Se-deficit, the 2D sheet becomes unstable and transforms to a nanowire. Our results on Se-deficient MoSe2 suggest routes toward engineering the properties of 2D transition Metal dichalcogenides by deviations from the stoichiometric composition.
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