In brief

By layering graphene over finely-grooved silicon surfaces and leveraging the Smith-Purcell effect to manipulate electron energy, researchers create a potential compact, efficient THz radiation source.

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A quantum leap towards reshaping connectivity

8 May 2024

A new approach to generating terahertz radiation offers a compact, tuneable and scalable solution for faster data transmission and improved imaging applications.

Imagine your home Wi-Fi network as a delivery service, transporting data 'packages' full of emails, videos and social media content through invisible airwaves. Today’s Wi-Fi technologies make use of radio frequencies to swiftly deliver these packages.

Now picture that delivery service cruising on a highway at ultrafast speeds, carrying truckloads of data with unmatched reliability even in challenging environments. This future wireless network could harness terahertz (THz) radiation: a form of electromagnetic radiation that sits between microwaves and infrared light.

“THz radiation can penetrate non-metallic substances such as clothing, paper and plastic without the ionising dangers of X-rays,” said Wenjun Ding, a Senior Scientist at A*STAR’s Institute of High Performance Computing (IHPC). This unique property also means that beyond communications, THz radiation can unlock new possibilities in security, manufacturing and biomedical research.

However, conventional sources of THz radiation are either too weak, too large or too expensive for everyday use. To better integrate THz-based technologies into home devices like Wi-Fi routers, we need THz emitters that are compact, tuneable and low-cost, Ding added.

In a collaboration between Ding and colleagues from IHPC, the Institute of Materials Research and Engineering (IMRE), Nanyang Technological University, and the Singapore University of Technology and Design, researchers examined one possible solution: a phenomenon known as the Smith-Purcell (SP) effect. When charged particles are beamed very closely and parallel to a periodic grating—a surface covered with fine, evenly-spaced grooves—some energy from those particles scatters off the grating, turning into longer-distance radiation.

Taking advantage of the SP effect, the team proposed laying two-dimensional (2D) quantum materials like graphene over a silicon-based periodic grating. At just one atom thick, the conductive graphene layer allows charge carriers, like electrons, to move freely across its surface, generating THz radiation with minimal energy loss.

In their study, the team pinpointed optimal conditions for generating THz radiation by finely adjusting the distance between an electron beam and the graphene layer. They also discovered that electrons within the graphene could became 'hot' or highly energetic: an effect they manipulated to enhance THz radiation intensity.

“With SP radiation, you don’t need an electron emitter to put out electrons at a minimum velocity; 2D materials can excite ‘slow’ charge carriers,” said Ding. “This approach significantly reduces the system’s complexity, making it highly suited for compact THz radiation sources.”

The team’s approach offers other exciting advantages: it’s highly tuneable, as they can adjust THz radiation frequency by modulating electron energy or changing the grating pattern. It’s also scalable enough to put on a chip, making it feasible to integrate into portable devices. “These properties could drive advancements in wireless communication, sensing and imaging,” Ding added.

Ding credited National Science Scholar Shengyuan Lu as the project’s main contributor, with experimental advice from IMRE Senior Principal Scientist Jinghua Teng and team; and IHPC Scientist Ayan Nussupbekov as its equal contributor, under the supervision of Wu Lin, an IHPC Principal Scientist II, and NTU colleagues. Moving forward, in a project led by Teng, the team is further developing the use of the SP effect in other 2D quantum materials for THz and infrared applications.

The A*STAR-affiliated researchers contributing to this research are from the Institute of High Performance Computing (IHPC) and the Institute of Materials Research and Engineering (IMRE).

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Lu, S., Nussupbekov, A., Xiong, X., Ding, W.J., Png, C.E., et al. Smith–Purcell radiation from highly mobile carriers in 2D quantum materials. Laser & Photonics Reviews 17 (7), 2300002 (2023). | article

About the Researchers

Lin Wu is an Associate Professor in the Science, Mathematics, and Technology Cluster at the Singapore University of Technology and Design (SUTD) and holds a joint appointment as Principal Scientist II at A*STAR’s Institute of High Performance Computing (IHPC). She received a BEng degree with first class honours (2005) and a PhD degree (2009) in Electrical and Electronic Engineering from Nanyang Technological University, Singapore. From 2009 to 2021, she worked as a computational scientist at IHPC. Her research interests include theory and modelling in nanophononics and nanoplasmonics, emphasising quantum technology and sensing applications. She has authored or co-authored two book chapters and ~80 refereed journal papers, including Optics Express, ACS Nano, Science, Nature Communications, Nature Photonics, Advances in Optics and Photonics, Advanced Optical Materials and Nano Letters. She also holds four United States patents.
Wenjun Ding is a Senior Scientist at A*STAR’s Institute of High Performance Computing, where she joined in 2012. She received her PhD in Optics from the Institute of Physics, Chinese Academy of Sciences in 2011. Her research areas are in high-power laser-plasma interactions, including radiation sources, particle acceleration, high energy density physics and plasmonics. She also conducts research in additive manufacturing (3D printing), optics from the skin and quantum machine learning. In addition to academic interests, some are closely relevant to medical and industrial applications.

This article was made for A*STAR Research by Wildtype Media Group