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| ▲ Flexible semiconductor boards symbolize the power of graphene. | 영어로 읽는 과학기사 On October 5, the Royal Swedish Academy of Sciences announced its selection of Prof. Andre Geim and researcher Konstantin Novoselov from Manchester University as the winners of this year's Nobel Prize for Physics.
The substance responsible for winning the honor is a new material called "graphene." Recently, for the first time in the world, a Korean research team succeeded in mass producing graphene, a highly sought after new material. The study, which was led by Prof. Lee Hyo-young from Sungkyunkwan University, was first published online in Nature Communications, a sister publication of the world renowned science journal, Nature.
Graphene, new material with unlimited potential
Graphene is a compound integration of carbon atoms that form a beehive shape. Individual carbon atoms integrate with each other to comprise graphene by sharing one and a half electrons couples with a neighboring carbon atom. While the one and a half electron couples tightly combine carbon atoms, electrons that are not engaged in integration can freely move around within graphene.
For this reason, in graphene, electrons can move around more than 100 times more freely than in silicon. And since graphene has a beehive shape, it is highly resistant to shock. Like the net, whose shape can change but whose linkage state does not when bent and pulled, the blank space in the hexagonal structure of graphene effectively absorbs shock. Graphene is more than 100 times stronger than steel in strength, and is so elastic that it can be extended by up to 20% of its surface. Moreover, even if it is bent or extended in such a way, it retains conductivity. Heat conductivity of graphene is more than 10 times that of copper, and the material is so transparent that nearly 98% of light can pass through it.
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The reason the science community is paying attention to graphene as enthusiastically as to present the discoverers with the Nobel prize is that the material has seemingly unlimited applicability due to these characteristics. Graphene can be used in various electronic devices, including touch screens that do not break even when folded or twisted, and solar cell panels. Its applicability is so extensive and diverse that even the Nobel laureates can scarcely predict the future this substance will bring about. Additionally, graphene can easily combine with other materials, and thus presents unlimited expandability.
Not only does it increase the strength of an existing material, it can also transform a material that does not conduct electricity into a conductor. An addition of 0.1 percent of graphene into plastic can increase the heat resistance of the latter by as much as 30 percent, and an addition of 1% can transform plastic into a highly conductive material. Given these characteristics, graphene effectively lives up to its reputation as a "new dream material."
Graphene is especially drawing attention in the semiconductor field. Silicon accounts for more than 90% of the conventional chip market because it is highly durable, cheap to acquire, and heat resistant. However, silicon semiconductors face limitations in further development due to the slow moving speed of electrons, and because it is difficult to produce them at micro levels below 10nm. In comparison, graphene boasts strong conductivity, and thus allows for the production of semiconductors that are far faster than conventional silicon circuit boards. Moreover, the material allows for the production of chips in diverse shapes and in transparent forms. Hence, the material can be used for producing all different types of electronic devices, including flexible computers that are wearable on one's wrist, electronic books that can be folded and carried freely, conveniently attachable and detachable electronic tags, and screens that can be folded for storage.
Mass production is key
Graphene has such ample potential for applicability, but remains unfamiliar to the layperson. one reason is that the mass production of graphene is not easy. Globally, only a handful of companies mass produce commercially viable graphene, and all of those are American. The reason mass production of graphene is difficult is due to the low yield from currently available production methods and poor consistency in quality.
There are four known methods used in graphene production: the cellophane tape method, which Prof. Geim and researcher Novoselov used when they produced graphene for the first time in the world; the chemical vapor deposition method, in which methane and hydrogen are streamed onto a metal surface; the Epitaxial method, in which graphene is produced by piling up silicon carbide layer by layer; and the chemical method, which uses the Oxidation-reduction reaction. Of these, the chemical method, which exploits the chemical reaction of graphite, holds the biggest commercial viability. In fact, the American companies known to have grapheme-making capacity produce the material using this method.
To chemically produce graphene, one has to oxidize graphite by treating it with a strong acid. When carbon reacts with acid, it produces graphite oxide, a substance in which the oxygen functional group is contained in carbon, including a hydroxyl group, epoxy group, carboxyl group, and lactol group. Graphite oxide is easily dissolved in aqueous solutions due to the oxygen functional group. By attaching this to a site or transforming it into a pattern as one needs, and then detaching the oxygen using a reducing agent, one can produce graphene in large quantities.
The chemical method is easy to use, and advantageous in mass production. Among other problems, however, since it entails a large volume of impurities, it lowers the graphene�s purity. The reason is due to inadequate reducing in the process of a reducing agent treatment. To address this problem, scientists conduct studies by using diverse reducing agents, including hydrogen sulfide, hydrazine, hydroquinone, sodium hydroxide, potassium hydroxide, and powered aluminum. Due to its applicability in a gaseous state as well as a liquid, hydrazine is widely used as reducing agent; but temperatures must be kept at 100 to 120 degrees Celsius during reaction processes with this material, and nitrogen impurities in the graphene are also created.
Prof. Lee's team made a breakthrough with the chemical method. The team successfully synthesized high quality graphene with virtually no impurities at room temperature(40 degrees), which is far lower than the temperature conditions required in the hydrazine method. The new method reportedly allows for production of graphene even at low temperatures of 10 degrees or below. The team used a new reducing agent that had never been used previously. The new method also allows for reactions in a gaseous state, and the production of flexible as well as hard materials. Moreover, the only by-products generated in the process are water and iodine, which are easily disposable. As such, the method allow for the production of high quality graphene.
The study has opened up the possibility to mass produce high quality graphene in Korea. The search team has registered a domestic patent already, and is taking similar steps in the U.S., Europe, China and Japan. It is also planning on transferring the technology to not only domestic producers but to overseas ones as well. In explaining the significance of his research, Prof. Lee said, "Not only can graphene drastically increase data processing speeds, something that has not been increased further with silicon, it will also play a major role in other fields, including the development of ultrahigh speed semiconductors, solar cells, and organic semiconductors. As our study has made it possible to mass produce graphene, Korea has laid the foundation to emerge as a powerhouse in the next-generation electronic materials industry."
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저작권자 2010.12.13 ⓒ ScienceTimes
