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

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.

Mitigation of Electromigration in Metal Interconnects via Hexagonal Boron Nitride as an Ångström‐Thin Passivation Layer

“…(Figure 3) The Raman spectra (Figure 3d) clearly indicated a characteristic E 2g phonon mode at 1366 cm −1 , which corresponds to the typical Raman mode for monolayer hBN. [41,42] It must also be noted that the E 2g peak for hBN on Cu is not observed due to the suppression of electronphonon coupling effects and the consequent quenching of the Raman signal. This phenomenon is not unique to hBN and Cu, but rather common in 2DLMs on metal surfaces.…”

Two-Dimensional Indium Selenide for Sulphur Vapour Sensing Applications

“…To characterize the samples, two methods were used. Starting with the optical contrast analysis of the samples [7,38,39] to achieve a first thickness estimation on a Zeiss (Oberkochen, Germany) Axio Scope.A1 microscope with an Axiocam ERc 5s Camera. These measurements were corroborated using micro-photoluminescence (µ-PL) measurements, as the PL response of the material depends on its thickness, being a more reliable but much more time-consuming method than the first [11].…”

“…Two-dimensional (2D) materials have been vastly studied in the last decade since graphene was first obtained [1] by micro-mechanical exfoliation from three-dimensional layered materials [2] or grown through methods like chemical vapour deposition (CVD) [3]. Among these new 2D materials, particular attention has been paid to transition metal dichalcogenides (TMDs) [4,5], hexagonal boron nitride (hBN) [6,7], and III-VI semiconductors [8][9][10]. Each one of these 2D materials has different properties from those of their bulk counterpart, due to quantum-confinement and surface effects [8,10,11], with promising opportunities in the fields of nano-optoelectronics [12][13][14], photovoltaics [15], optics [16], and energy storage applications [17,18].…”

Optical Inspection of 2D Materials: From Mechanical Exfoliation to Wafer‐Scale Growth and Beyond

“…Reproduced under the terms and conditions of the CC‐BY license. [ 67 ] Copyright 2019, The Authors. Published by MDPI.…”

“…f) Measured (solid symbols) and calculated (curves) optical contrast (OC) of h-BN having layer numbers from 1 (inset) to 38 on a 290 nm SiO 2 /Si substrate. Reproduced under the terms and conditions of the CC-BY license [67]. Copyright 2019, The Authors.…”