Hyperspectral Raman imaging using Bragg tunable filters of graphene and other low- dimensional materials Etienne Gaufrès, a,e Stéphane Marcet, b Vincent Aymong, c Nathalie Y-Wa Tang, a Alexandre Favron, c Felix Thouin, c Charlotte Allard, d David Rioux, a,b Nicolas Cottenye, a Marc Verhaegen b and Richard Martel a * Hyperspectral Raman imaging is presented as a powerful method to acquire quantitative as well as qualitative information on low- dimensional materials. The method is, however, not widely used due to limitations of the Raman scanning instruments. Here we present a hyperspectral Raman system based on Bragg tunable filtering that is capable of global imaging with significantly reduced acquisition time and improved sensitivity compared to scanning confocal Raman microscopes. The operation principles of the instrument are presented, and the performance is benchmarked using a calibrated carbon nanotube sample. Examples of various applications are shown to illustrate the abilities of the technique to characterize samples deposited on oxidized silicon substrates, including graphene stacks prepared by chemical-vapor deposition, exfoliated MoS 2 , and carbon nanotubes filled with dye molecules. The wealth of information available through this hyperspectral Raman imaging technique opens many new ways to probe the properties of complex low-dimensional materials. Copyright © 2017 John Wiley & Sons, Ltd. Keywords: Hyperspectral Raman imaging; Bragg tunable filters; graphene; carbon nanotubes; chalcogenides Introduction Raman spectrometry is a powerful approach to probe vibrations in molecules and solids, especially low dimensional solids such as graphene, carbon nanotubes, and exfoliated black phosphorus. It requires no special sample preparation and can be performed in situ inside transparent containers providing different environmen- tal, thermal, and pressure conditions. A Raman spectrum contains not only the vibrational fingerprints of the sample, but it provides also additional information, such as the symmetries and population distributions. As examples of typical applications, the local temper- ature of the sample can be estimated using the intensity ratios of the Raman Stokes and anti-Stokes peaks, [1] stress distributions in a solid can be evaluated by mapping the Raman shifts and polariza- tion characteristics of specific modes, [2–4] layer stacking information can be acquired through interlayer modes [5,6] and phase transitions can be monitored in situ using the Raman peaks associated to each phase. [7] In addition Raman spectrometry helps research by provid- ing information related to higher order resonance effects, which has given access to phonon dispersion, [8] defects or impurity scatterings, [9] doping, [10] number of layers [11] . As detailed on the succeeding text, the wealth of Raman signals in nanomaterials combined with new advances in optics and detectors for imaging spectroscopy have inspired our team to further develop the Raman techniques and improve the signal throughput for hyperspectral imaging. Over the years, Raman instruments have been modified and improved using different light filtering schemes, including inter- ferometry (e.g. FFT) and dispersive gratings, to perform sample analysis at different excitation wavelengths from near-infrared to ultraviolet. The recent advances in laser technology in terms of output power and linewidth coupled with the significant prog- ress in quantum efficiencies of the charge-coupled device (CCD) arrays and in interferometric filtering have further impacted the development of more complex Raman systems and significantly improved their performance. Because the spatial resolution is limited only by optical diffraction, confocal spectrometry has been implemented to probe various penetration depths with sub-micron resolution. The Raman spectrometer has also been combined to various mapping and imaging techniques in order to acquire high resolution images of a sample, giving in the same time local Raman measurements for identifying molecular * Correspondence to: Richard Martel, Regroupement Québécois sur les Matériaux de Pointe and Département de Chimie, Université de Montréal, Montréal, Québec H3C 3J7, Canada. E-mail: r.martel@umontreal.ca a Regroupement Québécois sur les Matériaux de Pointe and Département de Chimie, Université de Montréal, Montréal, Québec H3C 3J7, Canada b Photon etc. Ltd, Montréal, Québec H2S 2X3, Canada c Département de Physique, Université de Montréal, Montréal, Québec H3C 3J7, Canada d Département de Génie Physique, Polytechnique Montréal, Montréal, Québec H3C 3A7, Canada e Laboratoire d’Étude des Microstructures, UMR 104 CNRS-Onera, Châtillon, France J. Raman Spectrosc. (2017) Copyright © 2017 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/jrs Research article Received: 22 July 2017 Revised: 18 October 2017 Accepted: 18 October 2017 Published online in Wiley Online Library (wileyonlinelibrary.com) DOI 10.1002/jrs.5298