Fig. 6

Raman spectrum (a) and images (b–d), PCA spectrum (e) and images (f–h). The squared area in Fig. 5j of 3 μm × 3 μm was scanned and Raman spectra were collected under an objective lens of 100 × , integration time of 1 s for each pixel of 0.1 μm × 0.1 μm (to create a matrix of 30 × 30). (b, c) map the characteristic peaks of PA and TiO₂, respectively. (d) merges them together. (f–h) map/merge PCA intensities of PC1–PC3, as marked