Mirrors for slow neutrons from holographic nanoparticle-polymer   free-standing film-gratings
  We report on successful tests of holographically arranged grating-structures in nanoparticle-polymer composites in the form of 100 microns thin free-standing films, i.e. without sample containers or covers that could cause unwanted absorption/incoherent scattering of very-cold neutrons. Despite their large diameter of 2 cm, the flexible materials are of high optical quality and yield mirror-like reflectivity of about 90% for neutrons of 4.1 nm wavelength. 
J. Klepp, C. Pruner, Y. Tomita, K. Mitsube, P. Geltenbort, M. Fally
cond-mat.mtrl-sci