FIGURE 4.

Images (A, B), typical Raman spectra (C) and image (D), PCA images of PC1 (E) and PC2 (F), PCA spectra (G), and PCA image merging of PC1 and PC2 (H). The squared area in (A) of 30 μm × 30 μm was zoomed in as (B) and scanned. Raman spectra were collected under an objective lens of ×100, with an integration time of 1 s for each pixel of 1 μm × 1 μm (to create a matrix of 30 × 30). (C) Raman spectra of the mother silicone, to compare with three typical scanning spectra (1 s) collected from the marked positions in (B) and their average spectrum of 900 (30 × 30) spectra. The intensity image (D) is mapped at a characteristic peak of silicone at 2,900 cm⁻¹, after 10% color off-setting. After PCA, the loading coefficients of PC1–PC2 are mapped as images (E, F). (G) PCA spectra, with the mother spectrum as the reference. (H) merges (E, F), using 3D presentation and a white background, after normalizing the loading coefficients to 0–1.