期刊
NANO LETTERS
卷 19, 期 5, 页码 3098-3103出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.9b00504
关键词
Transition metal dichalcogenide; monolayer; charge density wave; anharmoncity; size-dependent properties; phonons
类别
资金
- CINECA award under the ISCRA initiative [HP10BLTB9A]
- PRACE [2017174186]
- EDARI [A0050901202]
- Spanish Ministry of Economy and Competitiveness [FIS2016-76617-P]
- Agence Nationale de la Recherche [ANR-13-IS10-0003-01]
- Graphene Flagship [696656-GrapheneCore1, 785219-GrapheneCore2]
At ambient pressure, bulk 2H-NbS2 displays no charge density wave instability, which is at odds with the isostructural and isoelectronic compounds 2H-NbSe2, 2H-TaS2, and 2H-TaSe2, and in disagreement with harmonic calculations. Contradictory experimental results have been reported in supported single layers, as 1H-NbS2 on Au(111) does not display a charge density wave, whereas 1H-NbS2 on 6H-SiC(0001) endures a 3 x 3 reconstruction. Here, by carrying out quantum anharmonic calculations from first-principles, we evaluate the temperature dependence of phonon spectra in NbS2 bulk and single layer as a function of pressure/strain. For bulk 2H-NbS2, we find excellent agreement with inelastic X-ray spectra and demonstrate the removal of charge ordering due to anharmonicity. In the two-dimensional limit, we find an enhanced tendency toward charge density wave order. Freestanding 1H-NbS2 undergoes a 3 x 3 reconstruction, in agreement with data on 6H-SiC(0001) supported samples. Moreover, as strains smaller than 0.5% in the lattice parameter are enough to completely remove the 3 x 3 superstructure, deposition of 1H-NbS2 on flexible substrates or a small charge transfer via field-effect could lead to devices with dynamical switching on/off of charge order.
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