The process of melting has long been of interest to scientists. In the case of indium antimonide (InSb), a semiconductor often used to study such processes, the first steps in melting take a few hundred femtoseconds, a quadrillionth of a second. But until recently, no one knew what happened after the initial stages of a phase transition.

Now, in a study led by SLAC researcher Aaron Lindenberg, an international collaboration of scientists has uncovered new clues about the first instants of this process. The results are published in the April 4 edition of Physical Review Letters.

The group used a laser to excite the sample and then measured the structure of the disordered liquid using short X-ray pulses from the Sub-Picosecond Pulse Source, a technique called "pump-probe." Lindenberg and colleagues found that the structure of the disordered liquid was far different from what one would have expected. Tiny atomic-scale bubbles, called nucleation events, form first and seed the process, a unique transient state of matter in which large fluctuations dominate the response of the material.

The group captured the process on a timescale 100 times shorter than any other previous X-ray study. The results give scientists a deeper understanding of how disordered materials behave on short timescales, and could lead to improved materials processing techniques, such as electronics manufacturing.

A.M. Lindenberg, S. Engemann, K.J. Gaffney et al., "X-ray diffuse scattering measurement sof nucleation dynamics at femtosecond resolution", Phys. Rev. Lett. 100, 135502 (2008)

To learn more about this research see the full scientific highlight at:
http://www- ssrl.slac.stanford.edu/research/highlights_archive/femtosecond_2008.html