Figure 2
From: Transformation of ACC into aragonite and the origin of the nanogranular structure of nacre
Nanoparticle crystallinity and composition. (A) Crystalline nanoparticles (rests of tablets and/or hillocks) over the interlamellar membrane (organic amorphous material) (HAADF). (B) Closer view of the area framed in A. The highest contrast (brightest area) corresponds to the core of the particle (long arrow). The contrast fades towards the lower edge of the same particle (large arrowhead). The nanoparticle to the right presents an intermediate contrast. Densely scattered type- one nanoparticles (2–5 nm) (small arrowheads) with some contrast appear covering the organic amorphous material. (C) Bright-field (BF) STEM image of B. The particle to the left has a crystalline core (long arrow) (indicated by lattice fringes and reflections in the FFT analysis). Its lower part (big arrowhead) does not show lattice fringes. Dashed rectangles indicate the areas where the FFTs come from. (D) Nanoparticle showing the crystalline area (lattice fringes and reflections) on the left and the surrounding amorphous material on the right (HAADF). Squares with dashed lines indicate the areas where the FFTs come from. Two EELS spectra from crystalline (a) and amorphous (b) areas are shown (background removed, deconvolved, normalized and smoothed). The areas where the spectra where obtained are indicated by solid squares. (E) Line scan EELS performed across the organic membrane (dashed line a) and a type-two particle (dashed line b). Only the particle with high contrast (12 nm in size) presented an intense calcium signal (b) (background removed, deconvolved,normalized and smoothed). The FFT from the whole image shows that no crystalline structure exists. (F) Densely scattered type-one nanoparticles (2–5 nm) (small arrowheads) over the organic membrane. FFTs show that nanoparticles have amorphous structure, unlike the bright lower right area, which has crystalline structure.
