Gallium Clusters are Too Small to Melt

Nanoscopic clusters of gallium atoms, consisting of as few as 17 atoms, melt at much higher temperatures than bulk gallium, according to recent research at the Indiana University. The observation runs counter to theoretical expectations of melting points for small clusters. In fact, current theory suggests that the melting point should fall as a cluster size is reduced, and that nanoscopic lumps of many materials should be liquid at room temperature. In previous work, the researchers (Martin Jarrold, 812-856-1182) discovered similar trends in the melting of tin clusters, but did not observe melting transitions directly. Instead they monitored the shapes of small clusters to determine their state. In the recent experiment, the researchers launched the gallium clusters through a high pressure collision cell where they were heated in collisions with a helium buffer gas. By monitoring the portion of dissociated clusters that exited the collision cell, the researchers could directly determine the clusters' melting temperatures. While bulk gallium melts at 303 K, thirty-nine and forty atom gallium clusters melt at about 550 K, and seventeen atom clusters show no sign of melting at temperatures as high as 800 K. No theoretical framework currently exists to explain the high melting temperatures of gallium clusters. The researchers explain that their measurements may have important implications for nanotechnology and material science. In particular, nanoscopic clusters may not sinter at low temperatures if they don't melt as predicted by established theory. (G. A. Breaux et al., Physical Review Letters, upcoming article)

CLARIFICATION: Last week's update, number 660, was incorrectly labeled as number 661 in some mailings. This Update is number 661.