(a) Raman spectra of the recovered diamond anvil for different sample regions and first-order Raman band splitting into a doublet band of 1316–1331 cm⁻¹. It is a consistent one-to-one match between the positions in SEM image (fig. 4(a)) for measurement and the Raman data. (b) The splitting of LO and TO in the first Brillouin zone. The inset corresponds to the Raman peak of the rightmost LO and TO.