Phase transitions — changes of matter from one state to another without altering its chemical makeup — are an important part of life in our three-dimensional world. Water falls to the ground as snow, melts to a liquid and eventually vaporizes back to the clouds to begin the cycle anew.
Now a team of scientists has devised a new way to explore how such phase transitions function in less than three dimensions and at the level of just a few atoms. They hope the technique will be useful to test aspects of what until now has been purely theoretical physics, and they hope it also might have practical applications for sensing conditions at very tiny scales, such as in a cell membrane.
They worked with single-walled carbon nanotubes, extremely thin, hollow graphite structures that can be so tiny that they are nearly one-dimensional, to study the phase transition behavior of argon and krypton atoms…
Phase transitions change the density of atoms. In the vapor form, there are fewer atoms and they are loosely packed. Liquid has more atoms and they are more tightly packed. The solid is a crystal formed of very tightly packed atoms. To determine the phase of the argon and krypton atoms, the researchers used the carbon nanotube much like a guitar string stretched over a fret. A nearby piece of conducting metal applied an electrical force to oscillate the string, and the scientists measured the current to “listen” as the vibration frequency changed — a greater mass of atoms sticking to the nanotube surface produced a lower frequency.
“You listen to this nano guitar and as the pitch goes down you know there are more atoms sticking to the surface,” Cobden said. “In principle you can hear one atom landing on the tube — it’s that sensitive.”
Besides providing a test bed for physics theories, the work also could be useful for sensing applications, such as nanoscale measurements in various fluid environments, examining functions within cell membranes or probing within nerves.
“Nanotubes allow you to probe things at the subcellular level,” Cobden said.
Bravo! Working at this level of basic research can be a reward unto itself.
You always hope to see translation of your work into something expansive, a dialectic of operability recognized and put to use with sophistication and expansion. But, properly designed, context understood, you enjoy the contribution made and the function of learning.