Whenever research topics were mentioned, Professor Lee Yong-hee, a chair professor at Sungkyunkwan University, seemed to sparkle with excitement. From graphene to carbon nanotubes to van der Waals materials, the driving force behind his decades-long research journey was surprisingly simple. On the 24th at the Korean Physical Society's spring academic conference held at the Daejeon Convention Center, Professor Lee said, 'It's fun, so I continue.'
The HCR designation attached to his chair professorship stands for 'Highly Cited Researchers,' a term published annually by the global academic information company Clarivate. It means that the number of citations of his papers is in the top 1% worldwide. Since 2018, he has been selected as an HCR in the top 1% of scientists each year.
Professor Lee is a top 1% researcher in the field of two-dimensional new materials. He has gained global recognition, particularly for his research on carbon nanotubes and graphene. Both carbon nanotubes and graphene have structures where carbon atoms are linked together in a hexagonal honeycomb shape. Graphene is a flat structure, while carbon nanotubes are cylinders made by rolling graphene. Both have the advantages of being strong and having excellent electrical conductivity.
In 2005, Professor Lee was selected as the first national scholar by the National Research Foundation of Korea and the Ministry of Education. Until recently, he led the NANO structure physics research team at the Institute for Basic Science, consistently producing excellent research results. In his keynote lecture that day, he introduced his past works and achievements on the two-dimensional material 'van der Waals materials.'
Between molecules, the negative charge of electrons induces a positive charge, resulting in an attractive force, known as van der Waals force. Professor Lee noted, 'Graphite is a form where several layers of graphene are attached, and they are held together by weak forces. This is exactly the van der Waals force, and these materials are called van der Waals materials.'
While researching graphene, Professor Lee developed an interest in other van der Waals materials with similar structures to graphite. 'The properties of van der Waals materials are completely different when they are monolayered compared to when they are in bulk. In that process, new physical phenomena emerge. I always ponder what new things can be done with two-dimensional materials.'
At one time, Professor Lee dedicated much time to researching carbon nanotubes. Carbon nanotubes attracted significant attention in the scientific community as next-generation electronic materials. However, there were many limitations in producing semiconductor devices. It was challenging to assemble devices, and the yield was low. Ultimately, he shifted his focus to two-dimensional materials. 'It wasn't an easy decision, and the research on two-dimensional materials didn't initially go well. But looking back, that transition was the decision that led me to where I am now.'
Professor Lee has researched van der Waals materials for a long time, but he mentioned that there are still many issues to resolve before they can be utilized as semiconductor devices. One of these is the issue of 'contact resistance.' If the connection between semiconductor devices and metals is not smooth, current does not flow well. Simply put, it's like a faucet leaking when there is a gap between a water pipe and the faucet.
Professor Lee said, 'To ensure that current flows well, the energy levels on both sides must be aligned.' He explained that in two-dimensional materials, this value varies by substance, making alignment difficult. He believes that adjusting the energy levels of van der Waals materials with external voltage can resolve the contact resistance issue. Professor Lee mentioned, 'My goal is to create semiconductor devices that are better than silicon using two-dimensional materials.'
In addition, he is also conducting research to increase the efficiency of solar cells that convert light energy into electricity to over 30%. Professor Lee noted, 'In existing materials, the efficiency of solar cells is seen to be limited to 34%. I believe that there is a possibility of surpassing that barrier with two-dimensional materials, and I am working on it.'
Another focus is the development of 'spin devices.' Spin refers to a particle's intrinsic angular momentum that is independent of its motion in quantum mechanics at the microscopic level. Spin devices operate not through electron movement like semiconductors but by utilizing the spins of electrons, allowing them to operate at lower power. Professor Lee's research team was the first to find two-dimensional materials suitable for use as spin devices, and they are currently preparing a paper. This research area has the highest commercialization potential among Professor Lee's studies.
Professor Lee mentioned that he has many hobbies. A former judo athlete, he enjoys exercising. He rides a motorcycle. However, he stated that his biggest love, both past and present, is research. 'I do it because I enjoy it. There's no excitement without research. People around me question why I'm so engrossed, but once I've committed to research, I aim to go as far as it takes.' When asked about his ultimate goal, Professor Lee replied, 'If I can create a technology that can change the world, that will be enough.'