Double resonance Raman scattering process in 2D materials

Raman spectroscopy is a fundamental tool for the characterization of two-dimensional materials. It provides insights into the electronic and vibrational properties of these materials and is particularly rich in features when the incident laser energy approaches the electronic energy transition of the material. Among these features, the double resonance Raman process provides important information on the electron, phonon, and electron–phonon properties. It was on the study of carbon-related materials that the double resonance bands sparkled showing their potential and, since then, have been deeply searched in the study of novel 2D materials. Here, the authors review the double resonance Raman process in 2D materials focusing on graphene and semiconducting MoS2highlighting the origin of the bands mediated by the two-phonon and phonon–defect processes. The authors discuss the observed properties of the double resonance bands and compare the processes for graphene and MoS2to find guiding principles for the appearance of double resonance bands. The authors also discuss the new findings of the intervalley scattering process in transition metal dichalcogenides. A brief discussion of the defect-induced bands in both materials is also presented.