Figure 4. SEM and TEM images of N_x–COFs.

(a) SEM images of N₀–COF, (b) N₁–COF, (c) N₂–COF and (d) N₃–COF indicating morphological variation along the series. (e) TEM image of N₂–COF showing hexagonal pores, with fast Fourier transform (FFT) of the marked area (red circle) in the inset. (f) TEM image of N₃–COF with enlarged Fourier-filtered image (upper inset) of the marked area and representative selected area electron diffraction pattern (lower inset). Scale bars, 5 μm (a,b,c,d); 50 nm (e and f); 20 nm (f, upper inset).