Looking inside three-dimensional (3D) silicon photonic band gap crystals
  We have performed an x-ray holotomography study of a three-dimensional (3D) photonic band gap crystal. The crystals was made from silicon by CMOS-compatible methods. We manage to obtain the 3D material density throughout the fabricated crystal. We observe that the structural design is for most aspects well-realized by the fabricated nanostructure. One peculiar feature is a slight shear-distortion of the cubic crystal structure. We conclude that 3D X-ray tomography has great potential to solve many future questions on optical metamaterials. 
W.L. Vos, D.A. Grishina, P.Cloetens, C.A.M. Harteveld, and P.W.H.   Pinkse
cond-mat.other cond-mat.mtrl-sci