Fig. 7

a BSE image of A0080. White squares show the analyzed area by TOF–SIMS. Dotted lines are corresponding to outlines for concentrated regions of CHO (pink), CHNO (blue), CHN (green), and CHO–Na (yellow) compounds, respectively. b Ion intensity of ¹²C⁺,¹²CH₂⁺, C₃H₉⁺, CNO⁺, and CHNO⁺ ions relative to ²⁸Si⁺ ions. c Relative intensity of CH^–, CN^–, CO₂^–,CO₃^–,CO₄^–, and C₃H₉^– ions to ¹⁶O^– from area A, area B and area C, shown in (a) respectively