Figure 3.

Two-dimensional small-angle X-ray scattering (SAXS) analyses of fossil and extant H. diversipunctata scales. (a,c) Unmasked SAXS patterns (original images 1340 × 1300 pixels) of fossil (a) and modern (c) scale. The false colour scale corresponds to the logarithm of scattering intensity. The concentric white circles denote the expected locations of the scattering peaks for the single diamond (Fd-3m) nanostructures. Scale bars, 0.05 nm. (b,d) Indexing the peaks of the azimuthally averaged profiles of the respective two-dimensional SAXS patterns in (a) and (c) and in electronic supplementary material figure S2, using the plot of the moduli of the hkl Miller indices of the Bragg peaks against the corresponding reciprocal lattice spacing S. The observed peaks (solid black circles) are shown alongside the theoretically allowed reflections for the single diamond (Fd-3m) and f.c.c. (F4-3m; in light grey) crystallographic space group symmetries. The linearity and zero intercepts of the plot confirm the cubic aspect of the nanostructures, and the slope gives an estimate of the lattice parameter. (Online version in colour.)