Carbon is one of the most important elements. It has unique properties and is the foundation of all life on earth. Pure carbon can be hard diamond or soft graphite.
Because this material is made from graphite and contains the basic feature of olefins-the double bond between carbon atoms, it is called graphene. In fact, graphene originally exists in nature, but it is difficult to peel off a single-layer structure. Layers of graphene are stacked to form graphite, and 1 mm thick graphite contains about 3 million layers of graphene. The adhesion between the layers is loose and easy to slide, making the graphite very soft and easy to peel off. A lightly stroked pencil on the paper may leave traces of several layers of graphene.
Scientists have conducted theoretical studies on graphene-like structures in the 1940s, but for a long time since then, efforts to produce single-layer graphene have been unsuccessful. Some people think that such a two-dimensional material is impossible at room temperature. Under stable existence. In October 2004, a paper published in the American "Science" magazine overturned this perception. Andre Heim and Konstantin Novoselov, who work at the University of Manchester in the United Kingdom, completed their "magic" with ordinary tape.
They used tape to stick the flakes from the graphite, which still contains many layers of graphene. But after repeatedly sticking 10 to 20 times, the flakes become thinner and thinner, eventually producing some single-layer graphene. This seemingly very simple and not high-tech method is not their first. Someone tried before, but failed to identify single-layer graphene.
Heim and Novoselov put the peeled thin slices on a silicon oxide substrate. The interference effect of light makes the thin slices appear colorful streaks under the microscope, just like the effect of an oil film on the water surface. Using this effect, they observed single-layer graphene. In this way, the first two-dimensional crystal material officially appeared. Later, some other two-dimensional materials were prepared, such as two-dimensional crystals of boron nitride and molybdenum disulfide.
Graphene has a special significance for basic research in physics. It enables some quantum effects that could only be discussed on paper before can be verified through experiments, such as electrons ignoring obstacles and achieving ghostly crossings. But what is more interesting is its many "extreme" application prospects. However, what kind of changes this two-dimensional carbon will bring to the human world cannot be predicted even by the researchers who have won the Nobel Prize.
There are three reasons: On the one hand, no matter whether domestic or foreign, there is no technically found industrial synthesis method to obtain large-area single crystal graphene. On the other hand, the downstream industry chain of graphene has not yet formed in the market, and the demand for graphene is the greatest. It is only the major scientific research institutes and laboratories, and no large amount of graphene has been put into industrial operation.
As early as 2010, researchers from Sungkyunkwan University in South Korea and Samsung Corporation produced a transparent and flexible display screen composed of multilayer graphene and a polyester sheet substrate. At that time, Hong Bingxi, a professor at Sungkyunkwan University and the corresponding author of the paper, proposed that their method could be used to manufacture graphene-based solar cells, touch sensors, and flat-panel displays. But he also admitted at the time that it was too early for large-scale manufacturing and commercialization-five years later, Hong Bingxi's method still remained in the laboratories of Samsung and Sungkyunkwan University in South Korea.
The last aspect is the cost of graphene preparation. Due to the inability to mass produce, the cost of graphene preparation has remained high, and the high cost has also hindered the pace of industrialization in the downstream market. Previously, the price of graphene was as high as 5,000 yuan/gram, which was several times more expensive than gold. "The bottle of something that is not surprising is more expensive than gold. A few grams of graphene powder is worth hundreds of thousands of yuan. When we fly on the plane, we are separated by several people for transportation, fearing that it will be confiscated by the security check." The startups studied used to describe it this way.
In Canada, Grafoid and the National University of Singapore established the world’s largest graphene research center (NUS), and launched a new production base in Ontario in 2014. This base of about 20,000 square meters mainly produces graphene powder. At that time, The person in charge of the company stated that they can mass-produce high-quality graphene at a low price. However, more than a year has passed, and there has not been any new news from this base.
Therefore, it is mainly technical issues that really hinder the large-scale application of graphene. Among them, the development of consistent and reproducible synthesis methods for low-cost, large-scale, and high-quality graphene is the biggest difficulty.
An interesting thing that people are familiar with is that Andre Gaim used scotch tape to get graphene. But what people don't know is that the graphene obtained by this method has a small size, generally between 10 microns and 100 microns, and has the disadvantages of low yield and high cost, and cannot meet the requirements of industrialization and large-scale production.
Later, the graphite oxide reduction method is one of the most commonly used methods for preparing graphene. However, this method mainly obtains graphene powder, which has many defects and poor electrical and mechanical properties. Concentrated sulfuric acid is needed to oxidize graphite, which is a difficult problem in industrial waste liquid treatment.
After that, people thought that it is not necessary to use graphite to prepare graphene, but only needs to try to make carbon atoms form a thin film. Chemical vapor deposition (CVD) emerged at the historic moment. This method introduces gases such as ethylene or acetylene into a reaction chamber and decomposes these gases at high temperatures. After cooling, carbon atoms are deposited on the surface of the substrate to form graphene. . Although CVD can meet the requirements for large-scale and high-quality graphene production on a large scale, the problem is that due to its high cost and complex process, the application of this method in the preparation of graphene is limited.
Due to the huge difference in preparation methods, the price between graphene powder and CVD film also differs by thousands of times. For example, 1 gram of graphene powder only costs less than 10 yuan, while 1 square meter of graphene film costs tens to hundreds of yuan, and its weight is actually less than 1 mg.
There is another main method-solvent stripping method. Since the entire liquid phase exfoliation process does not introduce any defects on the surface of graphene, it provides a broad application prospect for its application in the fields of microelectronics, multifunctional composite materials, etc. The disadvantage is also that the yield is very low.
Therefore, from an application point of view, graphene is currently in the story-telling stage. "In addition, the current industrial standards for the size, uniformity, and reliability of graphene in consumer electronics have not yet been determined, so the actual use of graphene in consumer electronics has not yet been shown." Zhu Hongwei believes that graphite At present, ene can make small-scale devices in the laboratory, but mass production and integration quality cannot be guaranteed. "At least there is no hope yet."
In fact, even Gaim himself has reservations about the current commercialization of graphene. Gaim believes that graphene is a primer that has driven the development of a wider range of two-dimensional materials. But for graphene, from the perspective of physics, it has reached a bottleneck, and unless there is a greater breakthrough in the future, it is difficult to make further improvements.
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