Past Winner
2005 NSERC Doctoral Prize

Bradley John Siwick

Physics

University of Toronto

If there were Oscars for physics research, Dr. Bradley Siwick would be the hands-down choice of the "Physics Academy" for best director. He'd also walk off the podium with best film and special effects, and be lauded as the next Scorcese or Coppola. But Dr. Siwick's film is only 3.5 trillionths of a second long. And his stars are microscopic. But it was a movie that had the scientific community on its feet: the first real-time, atomic-level images ever recorded of a solid substance melting, atom-by-atom.

"Producing a molecular movie was a Holy Grail of chemistry," says Dr. Bradley Siwick, a recent University of Toronto Ph.D. recipient and winner of a 2005 NSERC Doctoral Prize – one of Canada's premier graduate student awards.

His stunning directorial debut was all the more remarkable in that there was intense international competition to capture these fleeting glimpses of atoms in motion. The work is part of a field known as ultra-fast science. It's based on using recent advances in laser technology, combined with X-ray or electron pulses to capture stroboscope-like femtosecond (10^-15 seconds) glimpses of molecular motion, including the breaking and forming of chemical bonds. These direct observations, scientists believe, will help them understand the primary forces governing atomic behaviour.

This goal is what's driving Big Science projects in the U.S., Germany and Japan to build billion-dollar femtosecond X-ray light sources.

But Dr. Siwick was able to perform these experiments using only a desk-top laser system that he built in his University of Toronto lab, the equivalent of making a home movie that turns into a blockbuster. The achievement was touted internationally as a milestone and made the front cover of Science in November 2003.

Dr. Siwick's breakthrough, working with a team that included his Ph.D. supervisor, University of Toronto physicist Dr. Dwayne Miller, came from combining theoretical insights with his own strong sense of engineering to create a "camera" that uses electrons and how they're diffracted, or scattered, to make atomic-level movies.

The work began with computational modelling to overcome the technical hurdles that faced researchers using ultra-fast electron pulses. Left unchecked, the repulsive forces that act between negatively charged electrons will wash out details of the atomic motions and produce a “blurry” movie.

To surmount this obstacle he built a unique instrument, the first molecular movie camera, that enabled him to consistently produce electron pulses, and thus movie shots, below 500 femtoseconds.

While the pioneering 19th-century photographer Eadweard Muybridge chose a galloping horse as the subject for one of the world's first motion pictures, Dr. Siwick chose to film the melting of polycrystalline aluminium from a solid to a liquid as the world's first femtosecond flick.

"We captured the detailed atomic configuration of the material as it evolved from a solid to a liquid state in only 3.5 trillionths of a second," says Dr. Siwick, presently an NSERC postdoctoral fellow at the Institute for Atomic and Molecular Physics in Amsterdam.

In Amsterdam, Dr. Siwick is continuing to study fast atomic rearrangements, but this time in an even more common substance – water. He is hoping to determine how loose protons, always present in water, are transferred between individual water molecules.