Developing compact and high performance electron sources with silicon carbide

By harnessing the power of ultrafast lasers and nanofabrication techniques, nanoscale dielectric laser accelerators can make strides in ultrafast science and medical and high-energy physics. However, building a nanoscale accelerator requires a correspondingly small electron source.

To create such an electron source, Leedle et al. constructed two compact ultrafast electron injector designs using silicon nanotip emitters and silicon carbide electrodes.

In their first design, the team created a 96 keV electron source within a 25 mm radius footprint using an immersion lens. The second electron source, deemed the ‘shoe box’ for its size, is more flexible and includes an immersion lens and a separate solenoid lens. The silicon carbide electrodes enable this source to be run at a 19 keV/mm gradient, nearly double the gradient used in most electron microscopes.

The sources bridge the gap between current technologies. Flat cathodes can achieve thousands of electrons per shot but produce large beams, and ultrafast transmission electron microscopes start with up to 20 electrons per shot at the source but then filter out 95 percent or more to achieve beam sizes small enough to probe atoms.

“We’re almost exactly in the happy medium between those two,” said author Kenneth Leedle. “We have a sub-micron beam with 10 to 20 electrons per shot where you can explore a different application space like ultrafast electron diffraction on difficult-to-make 2D materials.”

The researchers aim to provide higher fields at the cathode to decrease the resulting beam size with the same number of electrons per shot. They believe these designs are feasible for other laboratories to make on their own.

Source: “High gradient silicon carbide immersion lens ultrafast electron sources,” by Kenneth J. Leedle, Uwe Niedermayer, Eric Skär, Karel Urbanek, Yu Miao, Payton Broaddus, Olav Solgaard, and Robert L. Byer, Journal of Applied Physics (2022). The article can be accessed at https://doi.org/10.1063/5.0086321 .