Impurity – Helium Condensates (IHCs) David M. Lee, Cornell University, DMR 0504683

1. Impurity – Helium Condensates (IHCs)David M. Lee, Cornell University, DMR 0504683 IHCs are created when a mixed jet of helium gas and an impurity gas (such as a nitrogen, deuterium or a noble gas) penetrates through the surface of superfluid helium. The resulting gel-like solid is composed of an assemblage of nanoclusters of the frozen impurity, separated from one another by thin layers of solid helium. The nanoclusters are 5-10 nm in diameter.  Some of the N2 or D2 molecules can be dissociated by exposing the incoming jet to an electrical (RF) discharge. The figure above shows the preparation of a sample containing nitrogen atoms and molecules. The green glow corresponds to decay of excited metastable states of N atoms over a half hour period. Below about 2 degrees Kelvin the embedded atoms are completely stable against molecular recombination.

2. David M. Lee, Cornell University, DMR 0504683 Applications: IHCs can host low temperature chemical reactions at much higher concentrations than materials. Large amounts of chemical energy can be stored in unpaired atoms trapped in IHCs. IHCs made of deuterium can efficiently cool neutrons to very low temperatures. Study of the formation of the nanoclusters within IHCs could lead to a better understanding of the formation of catalysts, which possess a similar structure but are made of precious metals. IHCs are assemblages of nanocrystalites of impurity molecules (red), each separated by a thin layer of solid helium (yellow). Education: Graduate student Ethan Bernard will receive his Ph.D this fall for study of these materials.