Recently, we reported our results on “realization of 2D metals at the angstrom thickness limit” in Nature [1], and we are glad to see that this work has sparked significant interests and lively discussions within both the scientific community and the general public. Thanks to Prof. Lin He at Beijing Normal University for inviting me to write a story behind this work—although it is a little bit early for me to do this since this work is very preliminary and I have no experience in such writing, I deem this task as a challenge and I would like to get over it. In this short essay, I will try to recall the whole process over the last ten years on this work and also provide some extensions, mostly on my personal experiences and perceptions, which are just for fun for those readers of Frontiers of Physics. “Do something new, do something different.” This is a group motto often mentioned by my PhD advisor, Prof. Enge Wang, during our group meetings in those old days. When I was young, I could not catch too much of its meaning; when I grew older, I gradually understood my PhD advisor’s expectations for his students. Then I quickly delivered this motto to my own group right after I set it up in IoP-CAS in 2008.
After many years of graphene [
2] research in IoP-CAS, I was feeling a bit discouraged around the year 2015. Everybody knows how difficult it is when working in a very hot and competitive field. Although we had been working very hard and published some important results (which we believed) on graphene then, things became difficult — we frequently saw similar results published even before we were summarizing our own. I realized that we had to do something new and something different.
Based on our relatively rich knowledge, skills, and practices on graphene, as well as monolayer MoS2 (another 2D material we have extensively studied since 2012), I personally felt that we should try to explore some new 2D systems that have interesting low-dimensional physical properties. Then, I delivered these thoughts to my students and let them try 2D metals (2DMs) first. Since 2015, several talented students of mine, Peng Chen (now a professor in Southern University of Science and Technology), Xiaobo Lu (now a professor in Peking University), Jian Tang (to be a professor in Zhejiang University), and Jieying Liu (now a postdoc still in my group) have stepped into this new field and performed some preliminary attempts. Unfortunately, Peng, Xiaobo, and Jian experienced setbacks quickly and switched to their other projects. Note that most of my students have multiple research tasks, because I think they have the ability to handle different things simultaneously. From 2016 to 2019, only Jieying was working on the 2DM direction, making progress little by little.
Since 2018, Jiaojiao Zhao joined my group as a PhD candidate and started lab activities in 2019. After a short period of training, I delivered this very hard task to Jiaojiao and let him work with Jieying closely. Since then, Jiaojiao has tried a lot of things, including using a hammer to thin a metal foil, a technique we borrowed from gold foil production process. However, it is far away from success in achieving even micrometer thick metal foils by these techniques and we must find a new way. Note that, in the very beginning of this 2DM project, we have abandoned the top-down strategy. The reason is simple: unlike graphite having a layered structure, the bulk metal does not and cannot be exfoliated into atomically thin 2D form like graphene. The direct growth technique is also not suitable, since such isolated 2D forms are in principle not stable. After several years of practice, we are aware that we have to use an atomic flat surface for pressing. In this case, it is possible to get the metal surface atomically flat. A turning point appeared around 2020; I was inspired by a video of copper forging, which is a conventional industrial technique for metal thinning. At the same period, Jieying had been working on another project which aims to direct wafer-bonding of monolayer MoS
2 on sapphire [
3]. Jiaojiao also worked with Jieying on this wafer-bonding project and learned many experimental skills from Jieying. I then let Jiaojiao try similar bonding experiments with metals involved. Quickly he made some progress, suggesting that this route is feasible! On some day’s group meeting, we saw the breakthrough results on 2DM of bismuth from Jiaojiao, we were all very excited!
However, things were slowing down from 2020 to 2021, mostly due to the COVID-19 pandemic. During that period, it was hard to get fully involved in the research. In July 2021, Luojun Du (my former PhD student) came back from Finland and rejoined the group as a professor. Luojun has good hands on experiments and very solid fundamentals. After his coming back, I suggested him to be a joint PhD advisor to Jiaojiao. Since then, he has been extensively advising Jiaojiao and played a critical role in pushing this 2DM research moving faster. Although we have overcome that threshold on realization of 2DMs, there are still a lot of things awaiting, like addressing what is the thickness limit for different kinds of 2DMs, what are the fundamental electrical and optical properties of them, and so on. With the help from other members in my group like Wei Yang (a professor in IoP-CAS), Dongxia Shi (a professor in IoP-CAS) and Na Li (a professor in Songshan-Lake Laboratory), Jiaojiao spent another three years to collect the whole data. Part of the data were drafted into a paper which was then submitted to Nature on 1 August, 2024 and accepted on 29 January, 2025, which happens to be the day of the Chinese New Year.
After 10 years of arduous exploration, finally, we took a crucial step to respond to our original aspiration, i.e., that we realized, for the first time, 2DMs with their thicknesses reaching the 2D limit. Personally, I deem this work as the opening of the Pandora’s box for the 2DM research and enabling others to step in due to its low-threshold. “There is plenty of room at the bottom!” − this work is just a beginning and many further studies are awaiting. It would be nice to see soon how 2DMs behave physically as compared to their bulk counterparts, arising from the 2D confinement effect, and to what extent such 2DMs could be applied for specific applications in various technological fields.
I am lucky that this research is regarded as a groundbreaking advancement, promising to usher in new possibilities across various domains such as materials science, electronics, and condensed matter physics. I appreciate all the reviewers of this work for their positive responses like “the authors’ achievement is innovative and opens an important research field”. After this work was online in
Nature on 12th March 2025, it has quickly attracted great interests from both scientific and technological communities, including
Nature News entitled “Move over graphene! Scientists forge bismuthene and host of atoms-thick metals” [
4],
Nature News & Views entitled “Metals squeezed to thickness of two atoms” [
5],
Nature Podcast entitled “Sapphire anvils squeeze metals atomically-thin” [
6], and also other media such as Global Times, New Scientist, EurekAlert!, China Daily, just to mention a few.
Below I also write something related to this research, and hopefully the readers in Frontiers of Physics can enjoy it.
Regarding the persistence on research − In a group reunion that occurred early this year and before the paper’s publication, Xiaobo talked about that he regrets not sticking to the 2DM studies. I asked him jokingly, “Would you like to spend 7 years to get your PhD degree?” He replied with a big laugh. I personally appreciate Jiaojiao’s 7-years hard-work, and I always told my students that everything will get a return if you are persistent. This is a nice example happened to Jiaojiao. Till now, I still believe in it.
Regarding highest-level research − Friends in this community always discuss what is the highest-level research. I have no answer; there are a thousand Hamlets in a thousand people’s eyes. But I shared with my students what are the happiest moments I have ever experienced. That is, when I made some important progress (I think) I would be too excited to be sleepy all night and have to work in the Lab all night. I call that feeling as the Unity of Heaven and Man. It is gratifying that I have already seen many of my students have the same experiences as mine.
Regarding the beauty of research − I personally enjoy works that simplify difficult things. An example is the discovery of graphene. Profs. Geim and Novoselov used a very simple technique, i.e., exfoliation graphite by scotch tapes, to produce graphene and studied its fundamental properties. I deem our work another example. A scotch tape would cost you several dollars; although our tools are a little bit expensive, i.e., ~50 k CNY, it is still affordable to almost everybody working in this field. Writing a News & Views in
Nature, Prof. Sanchez-Yamagishi highlighted our work “Their low-tech approach produces air-stable 2D crystals with dimensions greater than 100 micrometres, which is a substantial improvement over what can be made using more expensive and complex techniques” [
5].
Regarding interest-driven research − Our research project on 2DMs is mostly interest-driven. It is financially supported for sure, but the detailed research contents are not listed in any goal-driven research funding proposals. I am very thankful that this kind of research has lasted for almost 10 years and finally output something. During the past 10 years, I also felt quite a lot of pressure; if we ended it with nothing − it is kind of wasting money that came from our funding supports.
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