Inert-Gas Solids with Nanoscale Porosity

The structure and thermal properties of novel mesoporous inert-gas solids were studied by synchrotron x-ray diffraction. The materials were prepared by injecting a jet of helium containing dilute amounts of inert atoms and molecules (Ne, Kr, ${\mathrm{N}}_2$) into superfluid helium. The characteristic size of the constituent building blocks is $\sim 60Å$, and the density is $\gtrsim {10}^{20}\mathrm{impurity}$ atoms per c${\mathrm{m}}^3$. The Kr and ${\mathrm{N}}_2$ solids are stable outside of liquid He, up to temperatures above 10 K. These materials may find various applications as a new type of porous medium for fundamental physics, as well as in cluster physics, matrix isolation spectroscopy, and catalysis of low temperature chemical reactions.