Korean and Japanese scientists have succeeded in observing and controlling the phenomenon of charged particles moving in 1 trillionth of a second in real time. This method can also control energy conversion and chemical reactions at the molecular level, and is expected to be used to enhance the efficiency of organic light-emitting diodes (OLED) and solar cells in the future.
Kim Yoo-soo, head of the Institute for Basic Science (IBS) Quantum Transformation Research Center and professor at the Gwangju Institute of Science and Technology (GIST), noted on the 7th that he and Hiroshi Imada, a professor at GIST, have developed a 'THz (terahertz) -optical scanning tunneling microscope (STM)' technology that can observe in real time and rapidly control the moment when charge moves in a single molecule.
The research results were published in the international journal 'Science' on the same day. Researchers from the RIKEN (Advanced Industrial Science and Technology), Yokohama National University, the University of Tokyo, and Ulsan National Institute of Science and Technology also participated in the study.
Charge refers to the amount of electricity possessed by an object. A negatively charged particle is an electron, while a hole where an electron has vacated is a positively charged hole. During the process of charge movement, an intermediate state called 'excitons' is formed, where electrons and holes coexist. The performance of OLEDs and organic thin-film solar cells depends on how excitons are utilized.
However, the time spent in this intermediate state is very short at the level of picoseconds (1 trillionth of a second), making observation or control difficult with existing technology. The research team developed a THz-optical scanning tunneling microscope using terahertz (THz) light, which vibrates 1 trillion times per second.
The scanning tunneling microscope is a device that obtains atomic-level images from currents generated when a fine probe approaches the surface of a material. Terahertz light creates a strong electric field in moments shorter than picoseconds, allowing for ultra-fast manipulation of electron movement. The research team successfully applied terahertz light to the scanning tunneling microscope to control the movement of electrons and light emission in a single molecule in real time.
Previously, attempts were made to control excitons with optical scanning tunneling microscopy, but the method involved applying voltage to move electrons, which was relatively slow and risked damaging the molecules. There were also limitations in capturing the brief moment when electrons move. In contrast, the research team explained that using terahertz light allows for ultra-fast control by pushing electrons in the desired direction within a very short moment.
Thanks to this, it is possible to observe in real time not only the movement of electrons but also the process of exciton formation as electrons combine with holes and emit light. An exciton is a state where an electron and a hole attract each other but do not fully combine. During the annihilation process, it emits light, playing an important role in display technologies like OLED and advanced quantum material research. The researchers also developed a device called a 'terahertz phase shifter,' which can precisely control the shape of terahertz pulses.
The researchers stated that this is significant as it lays an important technical foundation for developing next-generation electronic devices. While existing electronic devices improved performance by analyzing only the final results, a technical basis has now been secured to analyze and optimize processes at the molecular level in real time. Additionally, this technology can also be applied to chemical reaction control and the development of next-generation measurement and sensor technologies.
Professor Kim Yoo-soo said, "The Korean and Japanese research teams have succeeded in collaborating like a single team for this research," adding, "This collaboration model is likely to become a benchmark for Korea and Japan to jointly maintain a global lead in advanced research in the future."
References
Science (2025), DOI: https://doi.org/10.1126/science.ads2776