Think the super slo-mo on ESPN is good? The London Center for Nanotechnology has filmed a nanometer-sized gold crystal at a billion frames per second, capturing the movement of electrons like never before. For comparison, a typical baseball pitch filmed at a billion frames per second — as opposed to the normal thousands of frames per second — would take nearly 16 years to watch.
Imaging electron activity in gold gives scientists a better understanding of how gold behaves under exotic conditions and could prove useful when adapting gold particles to new technologies.
To make their billion-fps movie, the experimenters hit the gold with a pulse of infrared light that heated the electrons in the gold atoms. As a result, the electrons started “ringing like a bell, ” said Jesse Clark, a postdoctoral researcher at University College who is lead author on the paper describing the experiment.
Next, the team used an X-ray laser at the SLAC National Accelerator Laboratory, called the Linac Coherent Light Source, to light up the vibrating electrons. The X-rays function like the flash on a camera to illuminate the scene and “freeze” all motion of the atoms in any sample, leaving only the electrons still moving.
By imaging the vibrations, the scientists were able to make some important observations. First, to the surprise of the scientists, the vibrations moved at supersonic speed, much faster than expected. As a result of this high speed, the vibrations seemed to start up everywhere at once, but this was a bit of an illusion, the same way that a supersonic boom from a jet appears to lag behind the plane. To explain the fast vibrations, the scientists determined that the infrared light had to have been transmitted via the electrons surrounding the gold atoms. Other theories suggested that the energy might move through both the electrons and the atom’s nuclei, but that doesn’t seem to have been the case.
The team used gold because it’s a stable element and generally “behaves well,” in experiments like this, Clark said, in that it doesn’t react easily with any chemicals around it. He said the team would also like to be able to image the vibrations in fabricated nanodevices or watch how the vibrations can alter the properties of materials especially when they undergo changes its structure.
The LCN team made a 3D movie of the images that show the details of the vibrations, which are on the scale of picoseconds (a millionth of a millionth of a second, or such a short time that light travels less than a millimeter).
The work is appearing in the journal Science.
Photo: Regions of contraction (blue) and expansion (red) on the gold nanoparticle in the UCL experiment. Credit: Jesse Clark / University College, London