He is Luo Da, who graduated from Peking University with a Ph.D., is currently working as a researcher at the Korea Institute of Basic Science and Technology, and will soon join the School of Science and Engineering of Hong Kong Chinese University (Shenzhen).
Recently, he published a Nature paper as co-corresponding author and colleagues.
Figure | Roda (Source: Roda)
In their study, they discovered a liquid alloy system containing atomic percentage 77.75% gallium, 11.00% nickel, 11.00% iron, and 0.25% silicon.
At a pressure of 1 atmosphere, and at a temperature of approximately 1025 °C, when the liquid alloy is exposed to a mixture of methane and hydrogen, diamond grains of hundreds of nanometers in size, as well as polycrystalline diamond films of millimeter size, can grow on the subsurface of the alloy.
The liquid alloy used in this case contains a small amount of silicon, which results in the prepared diamond containing silicon vacancy color centers. In the experiment, the research team observed a significant fluorescence emission peak at about 738nm.
A silicon vacancy color center is a point defect structured as one silicon atom replacing two carbon atoms in a diamond lattice and can be used as a stable single-photon source for quantum technologies such as quantum cryptography, quantum computing, and quantum communication networks.
In addition, due to the sensitivity of the silicon vacancy color center to local environmental changes, it is also expected to be used for nanoscale sensing, including magnetic field sensing and temperature sensing.
From the perspective of industrial application, the paradigm shift brought about by this preparation method may break the limitations of high pressure on equipment and production, allowing engineers to design a variety of reaction devices for the production of diamonds, which is expected to change the production method of diamonds, further reduce production costs and improve diamond manufacturing efficiency.
It is foreseeable that in the future, it may become easier to produce diamonds on a large scale, with the production of diamonds of different shapes (including fibrous and so on) as well as larger sizes of single crystal diamonds expected to become a reality.
The reviewers also commented: "This work is a major breakthrough in the field of diamond growth, which will greatly promote the understanding of the diamond growth process in the academic community, and has a wide range of applications in the fields of materials science and industry." ”
However, Luo Da also admitted: "This method of preparing diamonds in liquid metal under atmospheric pressure is more like a new concept at present, and there is still a long way to go before it is actually applied." ”
Compared with industrial application, as a scientist engaged in basic scientific research, Luo Da pays more attention to the impact that this diamond preparation method can bring to the academic community.
"It is expected that scientists and engineers in the field of diamond manufacturing will try to repeat our diamond growth process, and there may be new discoveries and even breakthroughs in the process," he said. ”
"We welcome this healthy competition and look forward to working with scientists and engineers around the world to better understand the growth of diamonds in liquid metal at atmospheric pressure, so as to better control the nucleation and growth of diamonds, resulting in higher quality, larger grain sizes and higher quantities." Roda said.
（来源：Nature）
Man-made diamonds are produced under mild conditions
Diamonds, an allotrope of carbon, have long fascinated scientists and enthusiasts for their exceptional hardness, brilliance and performance.
Diamonds in nature are formed at extreme high pressures (tens of thousands of atmospheres) and high temperatures (900 to 1400 °C) deep in the Earth's mantle, and are formed over millions or even billions of years.
In addition to their traditional use in jewelry, diamonds are used in a variety of industries due to their superior physical and chemical properties: from industrial cutting tools to advanced electronics to biomedical devices, diamonds play a key role in a variety of fields due to their unmatched durability, excellent thermal and electrical properties, and good biocompatibility.
In recent years, advances in materials science have led to breakthroughs in synthetic diamonds, which have expanded the use of diamonds to some extent and increased their accessibility.
In general, there are two conventional techniques that can be used to prepare man-made diamonds larger than one centimeter in size.
One is the chemical vapor deposition method, which can deposit large areas of single or polycrystalline diamond films.
The second is the high-pressure, high-temperature synthesis method, which simulates the extreme conditions of high temperature and high pressure in the deep part of the earth, and uses molten metal as a catalyst and solvent, with an appropriate temperature gradient, to make the dissolved carbon form a diamond.
Among them, under the premise of strict control of experimental conditions, a single crystal diamond with a volume of up to 1 cubic centimeter can be grown from diamond seed crystals by high pressure and high temperature in 5 to 12 days.
It is worth mentioning that the size of the diamond grown by this method is usually limited to about 1 cm due to the limitation of the size of the high-pressure, high-temperature components.
On the other hand, high-pressure, high-temperature technology is widely used, and Bain & Company's 2018 Global Diamond Industry survey report pointed out that high-pressure and high-temperature diamonds accounted for about 99% of all man-made diamonds for economic reasons and other reasons.
（来源：Nature）
Since 2018, Rhoda's current team has considered and decided to explore ways to produce man-made diamonds under mild conditions, mainly by reducing the pressure during preparation, such as down to one atmosphere.
However, the known paradigm is that in liquid metal catalysts, man-made diamonds can only grow at extremely high pressures in the gigaPascal range (typically 5-6 GPa, 1 GPa is about 10,000 atmospheres) and high temperatures of 1,300-1,600 degrees Celsius.
Therefore, from a basic science perspective, achieving diamond growth under low-pressure conditions means breaking the existing scientific paradigm.
At the same time, it will also raise more questions and challenges, including the dissolution and diffusion of carbon atoms in liquid metals, and how diamonds nucleate and grow in liquid metals.
According to reports, Professor Rodney S. Ruoff of Rodda's current team first came up with the idea of using liquid metal to grow diamonds under lower pressure.
In fact, the academic community has long concluded that the use of high-temperature molten liquid metal as carbon materials in a low-pressure environment can only be prepared, that is, only graphitic carbon materials can be prepared, and diamond structures cannot be prepared.
At the beginning of this study, Prof. Ruoff often discussed with Prof. Luo Da and Gong Yan, a PhD student in the group, how to proceed. They realized that the key to the project was the design and development of a suitable liquid metal system.
(Photo of Roda with Professor Rodney S. Ruoff and Gong Yan) (Source: Rodda)
In the early years, there have been many reports of the use of elemental metals as solvents, and the final carbon materials prepared are graphitic carbon. So, they set their sights on the liquid alloy.
With a melting point of about 30°C, gallium is liquid at near room temperature, and gallium can form homogeneous liquid alloys with many other metals and non-metals at relatively low temperatures. Therefore, they decided to choose gallium metal as the solvent in the alloy.
It has also been reported that the solubility of carbon in gallium, even when raised to temperatures above 1000°C, is close to zero.
In order to grow diamonds in liquid metal, they realized that they needed to add other solute metals to gallium to increase the solubility of carbon in the liquid alloy.
However, there are many types of metals with such properties to choose from, including iron, cobalt, nickel, magnesium, calcium, aluminum, manganese, titanium, etc.
At that time, the team tried several different combinations of liquid alloys, but the results were not satisfactory, and only graphitic carbon was prepared.
The turnaround came from an unexpected discovery. In the process of trying to prepare diamonds using liquid alloys, they occasionally add substrates.
On the one hand, I wanted to see if I could grow the diamond on the surface of the substrate, and on the other hand, I wanted to investigate whether the substrate had an effect on the growth process.
At one point, they used monocrystalline silicon wafers as substrates. During this period, Gong Yan placed gallium on the surface of a silicon wafer, then heated it to about 1000°C, and conducted a growth experiment under atmospheric pressure in a mixture of methane and hydrogen.
Surprisingly, when the growth was over, the wafers disappeared. After repeating the experiment, they observed that the silicon wafer dissolved into gallium at high temperatures, maintaining a homogeneous liquid phase, and the entire dissolution process was very fast.
Later, Prof. Ruoff, Roda and Gong Yan investigated the binary phase diagram of gallium and silicon and found that at a temperature of 1000 °C, the solubility of silicon in gallium is close to 15% of the atoms.
At the same time, they took into account that silicon and carbon can form silicon carbide, in which the cubic phase of silicon carbide has a very similar structure to diamond. So, does this mean that silicon has the potential to help diamonds nucleate in liquid metals?
As a result, the team turned to silicon as a solute of choice and continued to explore the composition of the liquid alloy.
One day in August 2022, they finally found a gallium-nickel-iron-silicon liquid alloy and prepared a polycrystalline diamond film for the first time.
In subsequent experiments, they also found that the nucleation density of the diamond was closely related to the amount of silicon in the liquid metal. In doing so, they also confirmed the nucleation of diamonds in liquid alloys by silicon.
In the experiment of growing diamonds, Roda inserted thermocouples into different positions of the liquid alloy, hoping to further optimize the experimental parameters by monitoring the temperature of different areas of the liquid alloy during the growth of diamonds in situ.
It was during this experiment that he discovered the existence of temperature gradients in the liquid alloy, a discovery that inspired him and Gong Yan to further examine the amount of carbon dissolved in different regions of the alloy.
Eventually, they and Prof. Ruoff proposed a temperature-gradient-induced model of directional migration of carbon from the high temperature to the low temperature region in a liquid alloy, which revealed to some extent the dynamic process of diamond growth in a liquid alloy.
It is worth mentioning that the team also found that liquid metal has some flexibility in composition. For example, diamonds can also be grown by replacing nickel with cobalt or gallium-indium mixtures instead of gallium.
（来源：Nature）
Not only to do it, but to do it systematically
When the first draft of the paper was submitted to Nature and went through the first round of external review, one of the reviewers suggested that the research group do some theoretical calculations to explain the growth mechanism of diamonds.
Another expert also mentioned theoretical calculations in the reviewer's comments, but he also pointed out that "the existing experimental evidence is clear, and the long time required to supplement the theoretical calculations may delay the publication of this important result, so the authors can choose whether to supplement the theoretical calculations." ”
After seeing the above opinions, Professor Ruoff, the corresponding author of the paper, strongly recommended that the team not only do it, but also do it systematically, in line with a rigorous scientific research attitude.
This is not only to reply to the comments of reviewers, but also to improve the work and deepen the understanding of the growth mechanism.
During the revision process, Professor Ruoff also suggested that everyone try to understand the growth mechanism of diamonds experimentally, in other words, the research group also did some experiments that were not required by the reviewers.
"With this, we discovered the process by which the dissolved carbon in the liquid alloy reaches supersaturation and causes diamond nucleation, and this discovery was also added to the revised draft of the paper." Rhoda said.
最终，相关论文以《1atm 压力下液态金属中钻石的生长》（Growth of diamond in liquid metal at 1 atm pressure）为题发在 Nature[1]。
Gong Yan is the first author, and Rhoda and researchers at the Korea Institute of Basic Science (KBS) Won Kyung Seong and Professor Rodney S. Ruoff are co-corresponding authors.
Figure | Related papers (source: Nature)
Previously, there had been a lot of work using liquid metal to catalyze the decomposition of methane, but all of them had only produced graphitic carbon structures, and Luo Da et al. found an unusual liquid metal.
Due to the low pressure conditions, the graphite structure is a thermodynamically stable phase. Therefore, the judges considered the preparation of diamonds at low pressure to be a remarkable achievement.
Currently, the team is designing new experimental methods to try to "capture" the "nucleation moment" of diamonds in liquid alloys.
They believe that by elucidating the nucleation mechanism of diamonds, it will help control the nucleation process of diamonds, and ultimately enable the preparation of large-size, single-crystal diamonds.
On the other hand, they are also considering adding some other dopants such as boron or phosphorus to the liquid alloy to try to prepare doped diamonds and diamonds with color center defects in a controlled manner.
Resources:
1.Gong， Y.， Luo， D.， Choe， M.et al. Growth of diamond in liquid metal at 1 atm pressure. Nature 629， 348–354 (2024). https://doi.org/10.1038/s41586-024-07339-7
Operation/Typesetting: He Chenlong