A news release from the University of Toronto (U of T) says that a team of chemists has successfully captured images of atoms during the melting of aluminum.
Chemists at the University of Toronto have captured atom-scale images of the melting process-revealing the first images of the transition of a solid into a liquid at the timescale of femtoseconds, or millionths of a billionth of a second.
The result is an unprecedented "movie" detailing the melting process as solid aluminum becomes a liquid. This new study, led by Professor R. J. Dwayne Miller of the Departments of Chemistry and Physics, received the prestigious cover position of the Nov. 21 issue of Science.
Here is this cover of Science (don't forget to purchase a copy) (Credit: Brad Siwick, U of T).
Femtoseconds are pretty small time intervals. How did they do a movie?
Since no camera shutter can open and close at the femtosecond time scale, the team built a special system using a laser and an electron gun inside a vacuum chamber. The energy of the laser's blast superheated small sections of the aluminum to over 1,000 degrees Celsius, exceeding the metal's melting point of 660 degrees Celsius.
Can this be useful for you? Probably not. But these chemists think they have a new valuable tool which will allow them to make atomic movies of other chemical reactions.
"It is one of the dreams of chemistry to be able to actually watch that as it happens, and we now have a technique that lets us do that," says Jason Dwyer, a graduate student in Miller's laboratory and a co-author of the paper.
Here is the abstract of this paper published by Science, "An Atomic-Level View of Melting Using Femtosecond Electron Diffraction."
We used 600-femtosecond electron pulses to study the structural evolution of aluminum as it underwent an ultrafast laser–induced solid-liquid phase transition. Real-time observations showed the loss of long-range order that was present in the crystalline phase and the emergence of the liquid structure where only short-range atomic correlations were present; this transition occurred in 3.5picoseconds for thin-film aluminum with an excitation fluence of 70 millijoules per square centimeter. The sensitivity and time resolution were sufficient to capture the time-dependent pair correlation function as the system evolved from the solid to the liquid state. These observations provide an atomic-level description of the melting process, in which the dynamics are best understood as a thermal phase transition under strongly driven conditions.
Sources: University of Toronto news release, via EurekAlert!, November 20, 2003; Science, November 21, 2003
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