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. 2017 Aug 30;7:9965. doi: 10.1038/s41598-017-08776-3

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© The Author(s) 2017

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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PL measurement of electron beam irradiated MoS₂ with varying irradiation dose and lattice spacing. (a) PL spectra of electron beam irradiated MoS₂ measured with 632.81 nm (1.96 eV) laser with 150.14 kW/cm² power density for the samples with different irradiation doses, where the dashed lines are the fitted peaks. As the electron irradiation dose increases, the quantum dot size increases²¹. Referring to (c), the bandgap reduces. (b) The extracted peak energy and peak intensity as a function of irradiation dose from the dashed lines in (a), where the black dots connected with the dashed line correspond to the left axis, and the blue bars correspond to the right axis. As the irradiation dose increases, the PL peak moves towards smaller energies. The horizontal dashed line shows the peak intensity of the original peak from pristine MoS₂. The samples with 44.70 fC and 178.78 fC irradiation dose have higher peak intensity than that of the pristine sample. (c) Calculated bandgap as function of quantum dot size $a$ with $L =$ 4.18 nm. The colored vertical and horizontal lines mark measured peak energies and the corresponding quantum dot sizes $a$ . The inset is the extracted quantum dot size $a$ as function of irradiation dose. By controlling the irradiation dose, sub-nanometer precision can be achieved. As the irradiation dose increases, the estimated size $a$ progresses towards 1.3 nm (1.5 nm in diameter), which is limited by the size of the focused electron beam (2 nm). (d) PL spectra of electron beam irradiated MoS₂ measured with 632.81 nm (1.96 eV) laser with 150.14 kW/cm² power density for the samples with different lattice spacing $L$ but identical point irradiation dose of 44.70 fC, where the dashed lines are the fitted peaks. (e) The extracted peak energy (bandgap) as a function of spatial distance $L$ from the dashed lines in (d). The red curve corresponds to calculated results using $a =$ 1.26 nm from data in (c). Note that the precision of the spatial distance, $L$ , is limited by the resolution of the irradiation system.