Team develops new way to generate powerful and focused X-rays using electron waveshaping

Scientists led by Nanyang Technological University, Singapore (NTU Singapore) have developed and simulated a new energy-efficient way to generate highly focused and finely controlled X-rays that are up to a thousand times more intense than those from traditional methods. The findings are published in the journal Light: Science & Applications.

This paves the way for ultra high-quality X-ray imaging that uses powerful X-rays for detecting flaws in semi-conductor chips accurately. The new method could also allow more focused X-ray imaging to be done for health screening while using less energy.

The novel method is based on computer simulations that shoot electrons at an ultra-thin material with highly ordered structures, such as graphene. The basic mechanism is similar to how X-rays are conventionally produced using X-ray tubes. But there is a twist: In the simulations, the wave-like patterns of how the electrons travel are "shaped" in a very specific way so that the particles' traveling path matches and overlaps with the highly structured positions of the material's atoms.

This theoretically results in X-rays that are emitted at much higher intensities than normal, and that can be finely controlled so that they are generated in either many different directions or in a single general direction.

Usually, when the fired electrons collide with the atoms of the material, the electrons become deflected and emit X-rays, in what is called bremsstrahlung or "braking radiation."

Bremsstrahlung contributes to most of the emitted X-rays in conventional methods of generating the radiation using X-ray tubes. But one problem is that the X-rays are not focused since they are emitted in different directions. Current methods try to address this by filtering the X-rays so that only those emitted in the desired direction are used. However, even these filtered X-rays are still fairly diffused.

An international team of scientists from the Singapore University of Technology and Design, Stanford University, Technion–Israel Institute of Technology, Tel Aviv University and the University of California, Los Angeles, led by Nanyang Assistant Professor Wong Liang Jie from NTU's School of Electrical and Electronic Engineering, developed a way to overcome these challenges in computer simulations, by changing the way the fired electrons travel.

Using computers, the scientists modeled electrons passing through a specially made plate that also has a current flowing through it to generate a voltage. The scientists were able to show in simulations that the way the electrons traveled changed after passing through such a "phase plate," an effect called electron waveshaping.

This happens because electron particles are able to travel in a wave pattern like light waves, according to quantum physics. As a result, earlier research has shown that they can interfere with one another after passing through a phase plate. The plate's voltage also causes shifts in the pattern of the electrons' wave-like movement, and adjusting the voltage can tweak the electron's wave pattern too.

The shaped electrons were then simulated to strike an ultra-thin material made of graphene about 1,000 times thinner than a strand of hair.

Due to how these electrons were shaped, the electrons' path of travel had a very high tendency to match the hexagonal positions of the atoms in graphene.

This increased the probability that the electrons would collide with the atoms and the simulations showed that more X-rays would be emitted as a result, thereby increasing the intensity of the radiation produced.

The simulations showed that the new method was more energy efficient too. Using the same amount of current to fire electrons, the X-rays produced by the researchers' method were up to a thousand times more powerful than those produced by conventional methods using X-ray tubes. The intensity of the radiation could also be adjusted by making changes to the phase plate.