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Optical Contrast and Raman Spectroscopy Techniques Applied to Few-Layer 2D Hexagonal Boron Nitride

1
Instituto de Ciencia de Materiales, Universidad de Valencia (ICMUV), P.O. Box 22085, 46071 Valencia, Spain
2
Institute of Physics, Academy of Sciences Czech Republic v.v.i, Na Slovance 1999/2, 18221 Praha 8, Czech Republic
*
Author to whom correspondence should be addressed.
Nanomaterials 2019, 9(7), 1047; https://doi.org/10.3390/nano9071047
Received: 29 June 2019 / Revised: 15 July 2019 / Accepted: 16 July 2019 / Published: 22 July 2019
(This article belongs to the Special Issue Optics and Transport on 2D Materials)
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Abstract

The successful integration of few-layer thick hexagonal boron nitride (hBN) into devices based on two-dimensional materials requires fast and non-destructive techniques to quantify their thickness. Optical contrast methods and Raman spectroscopy have been widely used to estimate the thickness of two-dimensional semiconductors and semi-metals. However, they have so far not been applied to two-dimensional insulators. In this work, we demonstrate the ability of optical contrast techniques to estimate the thickness of few-layer hBN on SiO2/Si substrates, which was also measured by atomic force microscopy. Optical contrast of hBN on SiO2/Si substrates exhibits a linear trend with the number of hBN monolayers in the few-layer thickness range. We also used bandpass filters (500–650 nm) to improve the effectiveness of the optical contrast methods for thickness estimations. We also investigated the thickness dependence of the high frequency in-plane E2g phonon mode of atomically thin hBN on SiO2/Si substrates by micro-Raman spectroscopy, which exhibits a weak thickness-dependence attributable to the in-plane vibration character of this mode. Ab initio calculations of the Raman active phonon modes of atomically thin free-standing crystals support these results, even if the substrate can reduce the frequency shift of the E2g phonon mode by reducing the hBN thickness. Therefore, the optical contrast method arises as the most suitable and fast technique to estimate the thickness of hBN nanosheets. View Full-Text
Keywords: Hexagonal boron nitride; two-dimensional materials; optical contrast; Raman spectroscopy Hexagonal boron nitride; two-dimensional materials; optical contrast; Raman spectroscopy
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Krečmarová, M.; Andres-Penares, D.; Fekete, L.; Ashcheulov, P.; Molina-Sánchez, A.; Canet-Albiach, R.; Gregora, I.; Mortet, V.; Martínez-Pastor, J.P.; Sánchez-Royo, J.F. Optical Contrast and Raman Spectroscopy Techniques Applied to Few-Layer 2D Hexagonal Boron Nitride. Nanomaterials 2019, 9, 1047.

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