Raman spectroscopy is one of the most extended experimental techniques to investigate thin-layered 2D materials. For a complete understanding and modeling of the Raman spectrum of a novel 2D material, it is often necessary to combine the experimental investigation to density functional theory calculations. We provide the experimental proof of the fundamentally different behavior of polar 2D vs 3D systems regarding the effect of the dipole − dipole interactions, which in 2D systems ultimately lead to the absence of optical phonons splitting, otherwise present in 3D materials. We demonstrate that non-analytical corrections (NACs) should not be applied to properly model the Raman spectra of few-layered 2D materials, such as WSe2 and h-BN, corroborating recent theoretical predictions (Sohier et al 2017 Nano Lett. 17 3758–63). Our findings are supported by measurements performed on tilted samples that allow increasing the component of photon momenta in the plane of the flake, thus unambiguously setting the direction of an eventual NAC. We also investigate the influence of the parity of the number of layers and of the type of layer-by-layer stacking on the effect of NACs on the Raman spectra.
I Z acknowledges the Swiss National Science Foundation research grant (Project Grant No. 200021_165784). M D L acknowledges support from the Swiss National Science Foundation Ambizione grant (Grant No. PZ00P2_179801). R R acknowledges support from the Ministerio de Economía, Industria y Competitividad (MINECO) under grant FEDER-MAT2017-90024-P and the Severo Ochoa Centres of Excellence Program under grant SEV-2015-0496 and by the Generalitat de Catalunya under Grant Nos. 2017 SGR 1506. X C acknowledges financial support by the Ministerio de Economía, Industria y Competitividad under grant TEC2015-67462-C2-1-R (MINECO/FEDER), the Ministerio de Ciencia, Innovación y Universidades under Grant No. RTI2018-097876-B-C21 (MCIU/AEI/FEDER, UE), and the EU Horizon2020 research and innovation program under Grant No. GrapheneCore2: 785219. C S and D I acknowledge support by the Swiss Nanoscience Institute (SNI), the ERC project TopSupra (787414), the European Union Horizon 2020 research and innovation program under grant agreement No. 785219 (Graphene Flagship), the Swiss National Science Foundation and the Swiss NCCR QSIT. J.M.-S. acknowledges support through a Clarín Marie Curie-COFUND grant from the Government of the Principality of Asturias and the EU (PA-18-ACB17-29), and the Ramón y Cajal Program (RYC2018-026196-I) from the Government of Spain. R T acknowledges support by European Union's Horizon 2020 research and innovation programme (SPQRel grant agreement no. 679183). K W and T T acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan and the CREST(JPMJCR15F3), JST.