Nanometre-scale clusters have very different physical and chemical properties from those of bulk crystals. For example, their unique magnetic, electronic and catalytic properties show great promise for a wide variety of applications. Although many techniques to make nanoclusters exist, producing these materials in large quantities remains a challenge.
Valery Kiryukhin of Rutgers University in New Jersey, together with colleagues at Cornell University, the Russia Academy of Sciences and the National Academy of Sciences of Ukraine, say that the impurity-helium gas injection technique (IHGIT) can be used to produce bulk amounts of nanoclusters. Previously, researchers believed that the materials made using this method were aerogel-like objects in which the nanoparticles were fused together. Using X-ray diffraction, Kiryukhin and colleagues have now shown that the samples contain individual nanoclusters isolated from each other by inert helium. This means that truly bulk amounts of individual nanoclusters can now be made for the first time.
In their IHGIT technique, the researchers inject a helium gas jet containing a small amount of another chemical species into superfluid helium. Nanoclusters, covered by protective coats of inert helium, are produced in the gas jet. The clusters can then be collected in bulk amounts inside the liquid helium.
"Our technique works for virtually any chemical species that can be added to the helium jet," explained Kiryukhin. "Bulk amounts of nanoclusters can therefore be produced for a large variety of materials. Other methods are either compound-specific or do not produce bulk amounts."
The nanoclusters could be used to study the fundamental structural and magnetic properties of nanoparticles. They might also be used as energy storage materials and efficient neutron moderators. Since these materials have a large surface area, they could find use in catalysis too.
The team will now study how the structures of their noble-gas clusters change at elevated temperatures. They also plan to investigate the structure of deuterium and nitrogen clusters in more detail as well as study new compounds, such as water.
The researchers reported their work in Phys. Rev. Lett..