This Optical Fiber-Based Electron Gun Can See Through Atomic Motion

This Optical Fiber-Based Electron Gun Can See Through Atomic Motion
Credit: Chiwon Lee

There are so many hidden discoveries for scientists to uncover, and one of them is how atomic motion looks like when observed directly at the time of structural changes. Atomic motion, the unknown “Holy Grail” of physical and chemistry experiments, created an entire research field because of all the chemical processes which act during this motion. A team of scientists has now successfully designed a super-fast optical fiber-based electron gun that can see through atomic movements and reveal them.

The transition state is exactly the point at which the reactant’s (the substance which goes through a chemical reaction) configuration and the product’s (the result of the chemical reaction) configuration are separated. Scientists didn’t know exactly what the transition state looked like, given the vast amount of different nuclear configurations. That left scientists confused about how some systems determine which reaction will take place.

Now a new study hints at “ultrabright” electron sources with enough brightness to light up atomic motion and show it in real time at a scale of 100 femtoseconds. In that case, those sources would be relevant to chemistry because atomic motion does really occur within that timeframe. Researchers at the Max Planck Institute for the Structure and Dynamics of Matter conducted the study and published their results in the journal Applied Physics Letters.

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“Detailed analysis reveals that the stretched optical trigger pulse owing to the dispersion effects inside the waveguide dominantly determines the temporal length of the low density electron bunch,” the scientists wrote in the abstract for their study.

They first observed the atomic movements of phase transition in bulk thin films. They used high-energy electron bunches, which caused them to wonder if they could cause atomic movement through surface reactions which would occur within the first few monolayers of materials. They then decided to develop an optical fiber-based electron gun for miniaturization. The gun is capable of stretching electron pulses and uses camera technology to obtain temporal resolutions within the low-electron energy routine.

“The first atomic movies use a stroboscopic approach akin to an old 8-millimeter camera, frame by frame, in which a laser excitation pulse triggers the structure, then an electron pulse is used to light up the atomic positions,” co-author Dwayne Miller said in a statement to “We believed that a streak camera could get a whole movie in one shot within the window defined by the deliberately stretched electron pulse. It solves the problem of low electron numbers and greatly improves image quality.”

Out of all the possibilities when it came down to nuclear configuration, the group found the system would go down to only a few key modes compatible with chemistry. They found that the reduction in such huge dimensionality happens during the transition state and can be concluded. The optical fiber-based electron gun will help researchers see through the transitions and reductions of the large space.

“We see it directly with the first atomic movies of ring closing, electron transfer and bond breaking,” Miller said.

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