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. 2017 Oct 19;7:13539. doi: 10.1038/s41598-017-13769-3

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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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Examples of the variation of the 2D band at different spatial locations. (a–c) illustrates from top to bottom decreasing 2D ₁ and 2D ₂ peak separation, change in relative intensity and varying peak energies. (d) shows a full spectrum with an inset of an optical image of the sample.