Graphene: the star of tomorrow's new material

In March of this year, Zhejiang University made use of graphene and other materials to make the world's "lightest material."

Want to download a high-definition movie in a second? The advent of graphene modulators may make this wish come true.

Professor Zhang Xiang, a Chinese-American scientist, used graphene to develop a modulator. This high-speed signal transmission capability, which is only a thin optical filter of four percent, is expected to increase the transmission speed of the Internet by 10,000 times.

Graphene is undoubtedly the most dazzling of all the "stars" of the material in the past ten years and even in the coming decades.

Although it has not been found for less than ten years, graphene has been causing a round of turbulence in the scientific and industrial circles. As people's understanding of it gradually became clearer, its mysterious veil was uncovered as much as it was at the beginning - thin and hard, good transparency, strong thermal conductivity, high electrical conductivity, stable structure, and electron migration speed. Fast, can observe the quantum Hall effect at room temperature...

From hypothesis to reality

Graphene is a basic unit material constituting a carbon allotrope such as graphite, charcoal, carbon nanotubes and fullerene, and is a two-dimensional crystal.

The structure of graphene has always been considered to exist only in theory and cannot be stably present alone. Until 2004, British physicists Andrei Heim and Konstantin Novoselov successfully separated graphene from graphite, confirming that it can exist alone.

Initially, the scientists peeled off the graphite flakes from the graphite, then glued the two sides of the flakes to a special tape and peeled the tape to split the graphite flakes into two.
Through repeated operations, the graphite sheets become thinner and thinner. Finally, they obtained a sheet consisting of only one layer of carbon atoms, which is graphene.

With the pioneering experiment in two-dimensional graphene materials, the two scientists jointly won the 2010 Nobel Prize in Physics.

The discovery of graphene is significant because it creates many “records”.

Graphene is the thinnest material in the world.

"Graphite is only 0.34 nanometers thick, and the thickness of 100,000 layers of graphene is roughly equal to the diameter of a hair strand. People can't see it with the naked eye." Deputy Director, Micro-Nano Manufacturing and System Integration Research Center, Chongqing Research Institute, Chinese Academy of Sciences Shi Haofei said this in an interview.

Graphene is the most intense substance known to man.

It is harder than diamonds and is 100 times stronger than the best steel in the world.

The physicist at Columbia University used diamond-made probes to test the graphene's ability to withstand. The maximum pressure that can be withstrated per 100 nanometers before the particles of the graphene samples were broken began to reach 2.9 micro-bottles. . This means, “If you use a graphene bag, you will be able to withstand about two tons of items.”

Graphene has extremely low resistivity and electron migration is extremely fast.

In graphene, electrons can migrate very efficiently, with a migration rate of only one-third of the speed of light, much higher than in conventional semiconductors and conductors such as silicon and copper.

“Electronics seem to have no mass in graphene, and the movement speed is very fast.” Zeng Changjun, a professor at the University of Science and Technology of China, said in an interview with the Journal of Chinese Journal of Science and Technology that “the electron energy will not be depleted, so that this material has Unusually good features."

Another feature of the material is to surprise the materials scientist. The material is almost completely transparent and has a light transmittance of over 97%.

In 2012, IBM USA successfully developed the first integrated circuit made of graphene wafers, which made the special electrical properties of graphene show the application prospects. Gao Hongjun, an academician of the Chinese Academy of Sciences, said: "Graphite materials have excellent electrical properties and are expected to be used in the manufacture of next-generation high-performance electronic devices."

Guiding the technological revolution

The mysterious and magical special properties of graphene make people full of illusions about its application.

In China, the application research on graphene is in full swing.

China is in the forefront of the basic research and industrialization of graphene, and many research teams have made breakthroughs in the performance research and preparation technology of graphene. Among them, the graphene film preparation technology of the Chongqing Institute of Green and Intelligent Technology of the Chinese Academy of Sciences was transferred at a price of 210 million yuan, which made researchers and developers eager to move.

Worldwide, the craze for graphene research and applications continues to surge.

According to statistics from Cambridge Intellectual Property Corporation, as of May this year, a total of 9,218 graphene patents have been approved and pending in the world, and the number of patent applications has increased fourfold in the past five years; since 2004, graphite The research papers in the field of olefins are exponentially increasing. The total number of papers has exceeded 20,000 so far, and in 2006 alone, it exceeded 6,000.

“Never a material has been widely watched in various fields like graphene.” Zeng Changyi felt that although there are no real graphene products available at home and abroad, “but it is the closest among many 'stars' materials. Applied materials."

Ultra-light body armor, ultra-thin ultra-light aircraft, ultra-thin foldable mobile phones, high-strength aerospace materials, high-performance energy storage and sensors, supercapacitors, and even more imaginative space elevators, more and more based on graphene materials Future devices enter the research field of scientists.

Among them, the application of transparent electrodes is the most attractive.

"Graphite has good electrical conductivity and light transmission properties, which makes it have a very good application prospect in transparent conducting electrodes." Zeng Changjun said that today's touch screens, liquid crystal displays, organic photovoltaic cells, organic light-emitting diodes, etc. are required in electronic products. Good transparent conductive electrode material.

The traditional conductivity electrode uses indium tin oxide, which is relatively brittle and is relatively easy to damage.

In contrast, graphene is not only harder but also better in performance.

“Indium tin oxide has a low light pass rate. With graphene, the screen of the display will be brighter.” Zeng Changjun told reporters that the application of graphene in transparent electrodes will greatly reduce the cost of electronic equipment and make it more energy-efficient. More clearly, “Graphene will certainly be commercially viable in terms of transparent electrodes within ten years”.

More than 97% of the light pass rate has revolutionized the application of transparent electrodes, and it has also made it possible to upgrade the solar industry.

According to experts, the current solar panels on the market are basically polysilicon, and its photoelectric conversion rate is about 30%, while the photoelectric conversion efficiency of graphene solar technology is as high as 60%, which is twice that of the existing polysilicon solar technology.

Recently, the Massachusetts Institute of Technology and Apple have released research reports on the possibility of using graphene as a solar cell to provide energy for electronic devices. Apple has filed a patent application for the purpose of carrying graphene solar energy in electronic equipment. The battery provides a solution.

Liu Zhaoping, a researcher at the Institute of Materials Technology and Engineering of the Chinese Academy of Sciences, said in an interview that the graphene microchip can form two-dimensional conductive contact with the active material particles of the lithium ion battery, and build a three-dimensional conductive network in the electrode, thereby greatly improving battery integration. performance.

Preliminary experimental results show that the lithium cobalt oxide battery with graphene conductive agent has a capacity higher than 3% and the discharge capacity has increased from 72% to 92% compared with the conventional battery.

Breakthrough preparation technology

The preparation technology is one of the roadblocks for graphene to enter the application field and realize industrialization.

Although domestic and foreign scientists have become more and more thorough in the research of graphene, the results of their application have also emerged. However, there are few real graphene materials available on the market.

The preparation technology is one of the roadblocks for graphene to enter the application field and realize industrialization. The high-cost preparation technology has pushed up the market price of graphene, and its price once reached 5,000 yuan per gram, which is more than ten times that of gold.

Gao Hongjun bluntly stated at the Xiangshan Science Conference on the topic of graphene held at the end of last year. China still faces great challenges in the research field of graphene preparation methods. “The challenge lies in how to prepare high-quality single-crystal materials with large areas and controllable impurity defects and how to improve the graphene processing technology of existing silicon-based processes.”

Despite this, Chinese scientists have still achieved major breakthroughs in the development of graphene preparation technology. Liu Zhaoping led the research team through years of efforts to develop graphene industrial preparation technology, reducing the manufacturing cost of graphene from 5,000 yuan per gram to 3 yuan per gram, directly bringing a large number of orders from foreign customers.

At the beginning of this year, the Chongqing Institute of Green Intelligent Technology of the Chinese Academy of Sciences announced the preparation of 15-inch single-layer graphene, and successfully applied a graphene transparent electrode to a resistive touch screen to prepare a 7-inch graphene touch screen.

It is worth mentioning that the above two research teams have jointly established a professional graphene production company with Shanghai Nanjiang Group to produce graphene microchips and graphene films respectively.

The research team of Zeng Changjun, the National Laboratory of Microscale Material Science, has taken a different approach. The conventional graphene growth based on gaseous carbon source needs to reduce the high temperature of 1000 °C to 300 °C, creating the lowest temperature for graphene chemical vapor deposition. .