Graphene for X-rays: Benchtop instruments

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  • Published: Apr 1, 2017
  • Author: David Bradley
  • Channels: X-ray Spectrometry
thumbnail image: Graphene for X-rays: Benchtop instruments

Seeking X-rays

A free electron ‘wiggled’ by graphene plasmons emits an X-ray pulse. Credit: A*STAR Singapore Institute of Manufacturing Technology.

A collaboration between the A*STAR Singapore Institute of Manufacturing Technology (SIMTech) and the Massachusetts Institute of Technology (MIT) in the USA is working towards a versatile, directional X-ray source that exploits the properties of the "two-dimensional" carbon material known as graphene and could be built as a bench-top or even handheld device for a wide range of applications.

It is well known that X-rays are high-frequency electromagnetic waves that can be generated using X-ray tube technology or with huge instruments such as synchrotrons with kilometre-long free electron laser systems. However, X-ray tube sources, commonly used in medical diagnostics, emit radiation in all directions, which means low efficiency. Moreover, such systems cannot be tuned for particular applications where a very specific frequency might benefit a particular analysis. Currently, different devices are needed for each frequency that a radiographer or researcher will need. Conversely, while free electron lasers can produce intense, tuneable X-rays by accelerating free electrons to extremely high energies and then wiggling them with a magnetic field, the enormous synchrotrons required are available in only a few large, expensive facilities around the world and not readily accessible to all. An X-ray source that is both small and powerful has been much sought after for some time.

Plasmon collaboration

To this end, the team of SIMTech-MIT researchers employed graphene, a one atom-thick sheet of carbon atoms, which, among other things, can support plasmons, collections of electronic oscillations that can be used to confine and manipulate electromagnetic radiation on the ten-nanometre scale.

With this in mind, the team first developed a powerful simulation that models the physics of electrons interacting with a plasmon field sustained on a graphene sheet deposited on a sheet of insulating, dielectric material. With numerous rounds of simulation, the team was able to demonstrate that this setup induces the requisite wiggling motion in electrons fired through the graphene plasmons, causing the electrons leading to the generation of high-frequency X-rays. The team explains that their simulations agreed with their analytical theory and explains how electrons and plasmons interact to produce X-rays in the first place.

Useful and tuneable

One particularly useful characteristic of such an X-ray source is that it is not only tuneable but can be pointed in a particular direction rather than generating X-rays in all directions. This will increase efficiency overall and so reduce costs by ensuring that the energy used in the system goes into generating useful X-rays rather than much of it being lost to shielding around the instrument. This will open up new avenues of research as well as making X-rays a more tenable medical treatments for targeting cancerous tumours, for instance, and so minimize peripheral damage to healthy tissues close to the tumour.

An even more attractive proposition with such a tool is its versatility. As the frequency of the output radiation can be tuned in real time from longer infrared rays to shorter X-rays by modifying various elements of the source, such as the speed of the electrons, the frequency of the graphene plasmons and the conductivity of the graphene, it could have many diverse applications in fundamental scientific and biomedical research. "Although there is a long way to go to actual realization, this is a very exciting research direction," explains Liang Jie Wong from SIMTech. "Developing an intense X-ray source that can fit on a table or be held in one's hand would potentially revolutionize many areas of science and technology."

Related Links

Asia Res News 2017, online: "Hand-held X-ray sources"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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