Figure 3.

Experimental schematic for SAXS experiments on feather barb nanostructures. A small (approx. 50 mm²) sample of the distal pennaceous portion of the feather vane is shown affixed to cover a 3 mm diameter hole on an aluminium block, which is then mounted in a plane perpendicular to the incident X-ray beam. The two-dimensional SAXS diffraction patterns for both channel- and sphere-type nanostructures exhibit ring-like features. Exploiting the circular symmetry of the SAXS diffraction patterns, the scattering intensity (I) is azimuthally averaged as a function of q to obtain scattering profiles, where the peaks correspond to the rings observed in the respective two-dimensional diffraction patterns. The scattering wavevector q measures the momentum transfer or the magnitude and direction of the scattering of incident photons (k_i into k_s) as a result of constructive interference from structural correlations of size 2π/q within the nanostructure.