X-Ray Studies of Structural Changes of Impurity-Helium Solids

We have performed studies of the formation and evolution of samples of Im-Helium (Im=Ne, D₂, N₂) solids obtained by allowing a mixed beam of helium and impurity molecules to fall onto the surface of superfluid helium. Clusters consisting of single impurity molecules and/or small aggregates of the molecules surrounded by layers of solid helium agglomerate to form porous solids. These solids have been studied by x-ray diffraction techniques. As the solids were heated above their formation temperature of T=1.5 K, the small aggregates or clusters of impurities tended to form larger clusters, which x-ray diffraction revealed to be nanocrystallites ranging in size from 3 to 6 nm.