Twinkle, Twinkle, Little Atom

November 2, 2012

In crystals, atoms are arranged in stable and well-order configurations that scientists can analyze with conventional X-ray techniques.  However, because atoms in liquids tend to change position rapidly and don’t have well-defined positions, researchers have had a hard time understanding liquid structures.

A new Argonne-led study at the SLAC National Accelerator Laboratory’s Linac Coherent Light Source (LCLS) may have helped to shed some light on this problem – quite literally. By using extremely short bursts of intense X-rays, a team of researchers from Argonne, McGill University, Boston University, DESY, and LCLS was able to investigate the “speckle” patterns that are generated when a coherent X-ray beam of light interacts with a material.

A familiar example of speckle is the shifting appearance of a laser pointer when it reflects from a rough surface, and it is also the same phenomenon that causes the appearance of “twinkling” of stars.  According to Argonne senior physicist Paul Fuoss, who worked on the study, there is a simple relationship between how the speckle pattern changes with time and the dynamic properties of the system under study.

“We really want to get a picture of the process by which materials transform from liquids to solids – either turning into crystals that are very ordered or glasses that are very disordered,” Fuoss said.  “We want to know what latent structures exist in a liquid that determine the direction it takes when it is cooled.”

While using the full beam produced by the LCLS would produce a detailed and crisp speckle pattern, Stephan Hruszkewycz, the lead author on the study, said that it would heat the sample by thousands of degrees.  “We had to strike a balance between getting a signal that we could extract data from and keeping our sample at the right temperature,” he said.