Graphene and perovskites make sensitive X-ray detector

Since Wilhelm Röntgen discovered them in 1895, X-rays have become a staple of medical imaging. In fact, barely a month after Röntgen's famous paper was published, doctors in Connecticut took the first ever radiograph of a boy's broken wrist.

There has been a lot of progress since. Aside from radiographs, which most people experience at least once in their lives, current medical uses for X-rays include fluoroscopy and radiotherapy for cancer. There is also computer tomography (CT), which involves taking multiple X-ray scans of the body from different angles and then combining them in a computer to generate virtual cross-sectional 'slices' of a body.

Nonetheless, medical imaging often works with low-exposure conditions, and therefore requires cost-effective, high-resolution X-ray detectors that can operate at what is called a 'low photon flux'. Photon flux simply describes how many photons hit the detector at a given time and determines the number of electrons it generates in turn.

Now, scientists led by László Forró at the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland have produced a novel version of just such a detector. Using 3D aerosol jet-printing, they developed a method for producing highly efficient X-ray detectors that can easily be integrated into standard microelectronics to considerably improve the performance of medical imaging devices. The scientists report their new detector in a paper in ACS Nano.

The new detector combines graphene, which is a single layer of carbon atoms in a honeycomb pattern, and perovskites, which are materials made up of organic compounds bound to a metal. Perovskites are versatile, easy to synthesize, and are at the forefront of a wide range of applications, including solar cells, LED lights, lasers and photodetectors.

Aerosol jet-printing is a fairly new process that is used to make 3D-printed electronic components like resistors, capacitors, antennas, sensors and thin-film transistors. It can even print electronics on a particular substrate, like the case of a cell phone.

Using the aerosol jet printing device at CSEM in Neuchatel, the researchers 3D-printed perovskite pillars on a graphene substrate. The idea is that the perovskite pillars act as the X-ray detector and electron discharger, while the graphene amplifies the outgoing electrical signal.

The research team used a methylammonium lead iodide (MAPbI₃) perovskite. MAPbI₃ has recently attracted a lot of attention because of its fascinating optoelectronic properties, which pair well with its low fabrication cost. "This perovskite has heavy atoms, which provide a high scattering cross-section for photons, and makes this material a perfect candidate for X-ray detection," says Endre Horváth, a chemist at EPFL.

The results were stunning. The method produced X-ray detectors with a record sensitivity that demonstrated a four-fold improvement on the best-in-class medical imaging devices.

"By using photovoltaic perovskites with graphene, the response to X-rays has increased tremendously," says Forró. "This means that if we would use these modules in X-ray imaging, the required X-ray dose for forming an image could be decreased by more than a thousand times, decreasing the health hazard of this high-energy ionizing radiation to humans."

Another advantage of the perovskite-graphene detector is that it is simple to form images using it. "It doesn't need sophisticated photomultipliers or complex electronics," says Forró. "This could be a real advantage for developing countries."

This story is adapted from material from EPFL, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

Since Wilhelm Röntgen discovered them in 1895, X-rays have become a staple of medical imaging. In fact, barely a month after Röntgen's famous paper was published, doctors in Connecticut took the first ever radiograph of a boy's broken wrist.

There has been a lot of progress since. Aside from radiographs, which most people experience at least once in their lives, current medical uses for X-rays include fluoroscopy and radiotherapy for cancer. There is also computer tomography (CT), which involves taking multiple X-ray scans of the body from different angles and then combining them in a computer to generate virtual cross-sectional 'slices' of a body.

Nonetheless, medical imaging often works with low-exposure conditions, and therefore requires cost-effective, high-resolution X-ray detectors that can operate at what is called a 'low photon flux'. Photon flux simply describes how many photons hit the detector at a given time and determines the number of electrons it generates in turn.

Now, scientists led by László Forró at the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland have produced a novel version of just such a detector. Using 3D aerosol jet-printing, they developed a method for producing highly efficient X-ray detectors that can easily be integrated into standard microelectronics to considerably improve the performance of medical imaging devices. The scientists report their new detector in a paper in ACS Nano.

The new detector combines graphene, which is a single layer of carbon atoms in a honeycomb pattern, and perovskites, which are materials made up of organic compounds bound to a metal. Perovskites are versatile, easy to synthesize, and are at the forefront of a wide range of applications, including solar cells, LED lights, lasers and photodetectors.

Aerosol jet-printing is a fairly new process that is used to make 3D-printed electronic components like resistors, capacitors, antennas, sensors and thin-film transistors. It can even print electronics on a particular substrate, like the case of a cell phone.

Using the aerosol jet printing device at CSEM in Neuchatel, the researchers 3D-printed perovskite pillars on a graphene substrate. The idea is that the perovskite pillars act as the X-ray detector and electron discharger, while the graphene amplifies the outgoing electrical signal.

The research team used a methylammonium lead iodide (MAPbI₃) perovskite. MAPbI₃ has recently attracted a lot of attention because of its fascinating optoelectronic properties, which pair well with its low fabrication cost. "This perovskite has heavy atoms, which provide a high scattering cross-section for photons, and makes this material a perfect candidate for X-ray detection," says Endre Horváth, a chemist at EPFL.

The results were stunning. The method produced X-ray detectors with a record sensitivity that demonstrated a four-fold improvement on the best-in-class medical imaging devices.

"By using photovoltaic perovskites with graphene, the response to X-rays has increased tremendously," says Forró. "This means that if we would use these modules in X-ray imaging, the required X-ray dose for forming an image could be decreased by more than a thousand times, decreasing the health hazard of this high-energy ionizing radiation to humans."

Another advantage of the perovskite-graphene detector is that it is simple to form images using it. "It doesn't need sophisticated photomultipliers or complex electronics," says Forró. "This could be a real advantage for developing countries."

This story is adapted from material from EPFL, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.