Recently demonstrated intrinsic antiferromagnetic topological insulator ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ has attracted wide attention, due to its elevated temperature for the observation of quantum phenomena, including quantum anomalous Hall effect and axion insulator states. However, the ongoing debate regarding layer-number determination and the surface layer degradation or reconstruction revealed by prior studies poses significant challenges for the in-depth exploration of the intrinsic properties of ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$. Here, we present a systematic study of Raman spectroscopy in few-layer ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ samples, which were freshly cleaved and protected in an inert atmosphere throughout the experiments, ensuring adequate sample protection. We establish one-to-one correspondence between layer number and low-frequency breathing modes based on the uncontaminated samples. Comparison of the Raman spectra between ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ and ${\mathrm{Bi}}_2{\mathrm{Te}}_3$, as well as between samples near and far from regions sectioned by focused ion beam (FIB), demonstrates that surface-layer degradation from ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ to ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ can be effectively prevented by avoiding air exposure and damage from the FIB. Our results provide a reliable reference for identifying the layer number and crystal structure. In this study, we provide a valuable benchmark for assessing the sample quality and pave the way for further realization on exotic topological phases of ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$.

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• Topological materials
• Layered crystals
• Inelastic light scattering