Phase Transition Studies Minimized to the Nanoscale

Phase transitions are among the most important natural phenomena that go on inside the large-scale, 3D world. The concept basically refers to the substances' abilities to change states (liquid, gas, solid) without having their chemical composition altered. One good example of this is the water's circuit in nature. But now researchers plan to use this knowledge in investigations conducted at the nanoscale, at the level of the individual atom, and inside hollow, atom-thick structures known as carbon nanotubes. They hope that this line of study will allow them to bring aspects of purely theoretical physics to life.

A group of physicists at the University of Washington (UW) believes it may have just developed the approach necessary to make this type of study a possibility. It devised an experimental setup in which it wanted to investigate the phase transition behaviors that occurred in argon and krypton atoms. “The physics can be quite different in fewer than three dimensions,” UW Associate Professor of Physics David Cobden says of the difficulties ahead. He is also the corresponding author of a new paper detailing the research, which appears in the January 29 issue of the top journal Science.

An additional difficulty lies in the fact that the team plans to conduct its investigations in less than three dimensions. This is why it is using nanotubes. Although these constructs do have a thickness, they are very close to being one-dimensional, about as close as possible with current technology. “For example, matter can freeze in 3-D and in 2-D, but theoretically it should not freeze in 1-D,” Cobden explains. He adds that the UW team, in essence, built a guitar string stretched over a fret. The CNT was stretched over a stretch of metallic material, which delivered electrical current, vibrating the tube.

As the tube vibrated, its oscillating frequency changed depending on how many atoms were inside. The number of atoms in the nanotubes is essential, as they dictate the phase transition state they can be found in. Lower-frequency vibrations dictate, for example, solids, or liquids, rather than gas. “You listen to this nano[scale] guitar and as the pitch goes down you know there are more atoms sticking to the surface. In principle you can hear one atom landing on the tube – it's that sensitive,” the team leader says. “Nanotubes allow you to probe things at the subcellular level,” he concludes.