In their quest to capture extremely fast atomic processes, scientists have made a big step forward using a superfast, high-resolution "electron camera," a newly developed instrument for ultrafast electron diffraction (UED), at the Department of Energy's SLAC National Accelerator Laboratory. Using the new electron camera, the team captured the world's fastest electron diffraction photos of nitrogen molecules rotating in a gas.
With a shutter speed of 100 quadrillionths of a second, the new achievement is something that scientists have long dreamed of but have never been able to accomplish due to instruments failing to have a combination of speed and detail.
"Our new UED instrument can do both: It achieves an unprecedented combination of atomic resolution and extraordinary speed," said Xijie Wang, co-author of the study and a researcher from SLAC's UED team. "We've taken UED snapshots of atomic motions in gases faster than ever before and demonstrated the technology's potential for making molecular movies of chemical reactions."
The UED utilizes a focused beam of energetic electrons and uses them to probe samples. In the current study, the team examined a stream of laser-excited nitrogen gas, an ideal system for studying chemical processes.
The beam sends electrons scattering off of the atoms in the sample, creating a pattern that researchers can detect and use to determine where the atoms in the sample are located. Using time variations for both the laser excitation and electron beam, scientists can use UED to determine the motions at the atomic level.
UED is not new, having been developed in the 1980s, but never before has it been accomplished at such a high speed for gases.
"When it comes to studies of gases, SLAC's instrument is about five times faster than any other UED machine before," said Jie Yang, co-lead author of the study from the University of Nebraska, Lincoln. "This leap in performance is due to the instrument's superior high-energy electron source, which was originally developed for SLAC's LCLS. It will help us better understand a whole new range of speedy processes on the atomic level."
The team used this leap in performance to capture the rapid rotation of nitrogen molecules in gas. After hitting them with laser pulses, causing them to briefly point in the same direction, the nitrogen molecules eventually fall out of alignment. However, eventually they line up in the same direction again and, using UED, they were able to capture these brief moments, also referred to as "molecular echos."
"When the nitrogen molecules do line up again, they also rapidly switch from pointing in one direction to pointing in the perpendicular direction," Yang said. "This transition takes only 300 quadrillionths of a second."
The findings were published in the April 5 issue of Nature Communications.