Carbon nanotubes: a "maverick" wonder material

2020-03-23 10:49 Zhu liman, zhang aimin

Do you know what the blackest material in the world is? Recently, researchers at a foreign college have created a material using carbon nanotubes that can absorb 99.96 percent of incoming light, making it the "black hole" in the material family. Similarly, using more than 14,000 carbon nanotubes, the researchers created a 16-bit microprocessor chip that says "Hello, World" to the World.

Carbon nanotubes, as a one-dimension quantum material with a special structure, possess many extraordinary mechanical, electrical, thermal and other physical and chemical properties.

The diagram shows the structure of carbon nanotubes. Photo: liu cheng

"King of materials" with excellent performance

Before the advent of carbon nanotubes, silicon was the king of the semiconductor family. The core of every existing transistor is a semiconductor component made of silicon. Depending on the "on" and "off" states of the transistor, it is shown whether current is passing through, thus presenting the "computer language" of 1s and 0s in the computer. However, the development of silicon transistors is facing a bottleneck in terms of size and performance, so people will pay more attention to the emerging materials such as carbon nanotubes.

Carbon nanotubes, also known as bucky tubes, are concentric tubes made up of layers or dozens of layers of carbon atoms arranged in a hexagonal pattern, with diameters ranging from 2 to 20 nanometers. The diameter of the nanotubes is only a few millionths of that of a human hair, and the thinnest reported is 0.4 nanometers in diameter. It is because carbon nanotubes are almost as thick as atoms, and because they transmit electricity so well, that they can be used to make better semiconductors than silicon.

Research shows that carbon nanotube processors can run twice as fast as silicon processors, but consume only one-third as much power as silicon processors.

In fact, carbon nanotubes have a number of magical properties that can be called "mavericks." As the material with the best mechanical properties, carbon nanotubes have extremely high tensile strength, young's modulus and fracture strain. Compared with the high strength steel of model ASTMA228, the nanotubes are 270 times stronger, about five times more elastic and a sixth as dense.

In addition, carbon nanotubes are superior to traditional conductive materials in electricity, heat and optics. Carbon nanotubes are, in theory, 10 times more efficient at conducting electricity than silicon, and once they are widely used, silicon valley may be a misnomer.

Taming carbon nanotubes is particularly difficult

The discovery of football-structured fullerenes in 1985 drew worldwide attention. Based on the "football" structure, carbon nanotubes with hollow cylindrical structures can be formed with minor modifications. Carbon nanotubes were first discovered in carbon fibre by Japanese researchers in 1991. Subsequently, the researchers found many properties such as excellent conductivity of carbon nanotubes. At present, efforts are being made towards the mass preparation of single carbon nanotubes with a length of more than meters or even kilometers.

It is not easy to tame the king of materials: carbon nanotubes. Although carbon nanotubes are semiconductors, they are currently made using metal, which inevitably gets mixed into the finished material. At the same time, converting carbon nanotubes into electronic components requires placing them in extremely precise positions. At present, there is no way to make carbon nanotubes grow in specific places. Carbon nanotubes also put forward very high requirements for the "delivery room" where they are "born" : once the ambient temperature is too high to make the catalyst inactive, carbon nanotubes will stop "growth"; On the contrary, if the control is slightly wrong, the carbon nanotubes will "grow like crazy".

In fact, back in 2013, researchers built the first computer with 178 transistors, each containing about 10 to 200 nanometres long. Today, computer transistors with a diameter of about 1 micron have been developed that can be switched on and off about 1 million times per second. In addition, the researchers also found that carbon nanotubes have excellent hydrogen storage properties, which are expected to be used in the manufacture of hydrogen batteries, and can be widely used in electric vehicles, submarines, electric locomotives and other fields.

There are also plans to twist tens of thousands of carbon nanotubes together to form a macro-fibre, known as the "ultimate fibre", which will be of strategic importance to the development of high-end technology in the 21st century. Once a breakthrough is made in the field of "taming" carbon nanotubes, a technological revolution that started with them is about to explode the world.

CNT could change the world

The creation of a "space ladder" between the earth and the moon or a space base has appeared in science fiction, including the three-body problem. To build a moonlit "space ladder", one needs to find a material that can span 380,000 kilometres without being pulled apart by its own weight. Carbon nanotubes, one of the most mechanically powerful materials ever discovered, have extremely high tensile strength and could help humans crawl from earth into space. In the future, humans may be able to get to and from space or the space station as easily as an elevator.

Also aided by the unique mechanical properties of carbon nanotubes, researchers are trying to develop "black tech" products such as "unbreakable" ropes, "unbreakable" fabric and "impervious" body armor. Wind turbines use blades that require extremely high strength and stiffness, and reinforced composites made from carbon nanotube fibers will be the best choice. Carbon nanotube fiber reinforced composites also have excellent fatigue resistance, and their applications in Bridges and buildings can not only improve their strength and seismic resistance, but also extend their service life. In the future, carbon nanotubes could be used for golf clubs, fishing rods, tennis rackets, bicycles, cars and high-speed trains.

By storing energy in carbon nanotubes, an iron man-like device could become a reality. At present, a foreign laboratory is leading the research and development of a new type of clothing that can provide electricity. The clothing, which turns carbon nanotubes into textile fabrics, will provide electricity for lighting, night vision and communications equipment used on the battlefield, further reducing the burden on individual soldiers.

In addition, by synthesizing carbon nanotubes, some researchers have developed a sensor fabric that can sense pressure changes sensitively, which can play an important role in the field of sports training. Carbon nanotubes are also being tried as a transparent, electrically conductive film as an alternative to touch screens.