Graphene is a two-dimensional crystal. Its structure is very stable because carbon atoms are arranged in hexagons and connected to each other to form a carbon molecule.
Graphene transistor was brought to people's attention by the 2010 Nobel Prize in Physics. In 2004, Professor Andre Heim and Konstantin Novoselov of the University of Manchester in the United Kingdom stripped graphene from graphite flakes in a very simple way, for which they also won the 2010 Nobel Prize award in Physics.
Graphene is a two-dimensional crystal. Its structure is very stable because carbon atoms are arranged in hexagons and connected to each other to form a carbon molecule. As the number of connected carbon atoms continues to increase, this two-dimensional carbon molecule plane is expanding, so does the molecule. A single layer of graphene has a thickness of only one carbon atom, that is, 0.335 nanometers, which is equivalent to one-thousandth of the thickness of a hair. There are nearly 1.5 million layers of graphene in 1-millimeter thick graphite. Graphene is the thinnest material we have known and has the advantages of extremely high specific surface area, superconductivity, and strength.
The processing limit of silicon materials is generally considered to be a line width of 10 nanometers. Constrained by physical principles, it is unlikely to produce products with stable performance and higher integration after less than 10 nanometers. However, the new transistor invented by British scientists will extend the life of Moore's Law. The transistor is expected to bring breakthroughs in the development of new ultra-high-speed computer chips. It is worth mentioning that the main developers of the world's smallest transistors were also the ones who developed graphene in 2004. They are Professor Andre Geim (Department of Physics and Astronomy, University of Manchester, UK) and Researcher Kostya Novoselov. It was because of the development of graphene that they were nominated for the 2008 Nobel Prize in Physics.
The world's smallest transistor, developed by British scientists led by the two, is only 1 atom thick and 10 atoms wide. The material used is graphene composed of a single atom layer. Graphene, as a new type of semiconductor material, has received widespread attention in the scientific community in recent years. British scientists use a standard transistor process to first etch a channel with an electron beam on a single-layer graphite film. Then, electrons are sealed in the remaining central part called the "island" to form quantum dots. The structure of the gate part of the graphene transistor is more than 10 nanometers of quantum dots sandwiched by a few nanometers of insulating medium. Such quantum dots are often called "charge islands." Since the conductivity of the quantum dot is changed after the voltage is applied, the quantum dot can memorize the logic state of the transistor like a standard field-effect transistor. According to another report, the research team led by Professor Andre Heim of the University of Manchester, UK had developed a 10-nm practical graphene transistor. Their latest research results that have not yet been announced is that they had developed a smaller graphene transistor with a length and width of one molecule. The graphene transistor is actually a transistor composed of a single atom.
Magical semiconductor materials
One of the graphene developers, Dr. Novoselov of the University of Manchester, pointed out that graphene is a "gold mine" in the research field, and for a long time, researchers will "mined" new research results.
So what is graphene? Graphene is a single-layer carbon atom thin film peeled from a graphite material. It is a honeycomb two-dimensional crystal composed of a single layer of hexagonal cell carbon atoms. In other words, it is a single-atomic layer of graphite crystal thin film whose lattice is a two-dimensional honeycomb structure composed of carbon atoms. The thickness of this graphite crystal film is only 0.335 nanometers, and its 200,000 pieces of film are superimposed together, which is only equivalent to the thickness of a hair strand. This material has many novel physical properties. Graphene is a zero bandgap semiconductor material with much higher carrier mobility than silicon, and theoretically, its electron mobility and hole mobility are equal, so its n-type field effect transistor and p-type field-effect transistors are symmetrical. In addition, because it has zero bandgap characteristics, the average free path and coherence length of the carrier in graphene can be micron-level even at room temperature, so it is a semiconductor material with excellent performance. In addition, graphene can also be used to make composite materials, batteries/supercapacitors, hydrogen storage materials, field emission materials, and ultra-sensitive sensors. So researchers scramble to invest in research on how to prepare and characterize their physical, chemical, and mechanical properties.
One of the reasons why scientists are interested in graphene is that they are inspired by the research results of carbon nanotubes. Graphene is likely to be a substitute for silicon. In fact, carbon nanotubes are graphene microchips rolled into the cylinder. Like carbon nanotubes, they have excellent electronic properties and can be used to make ultra-high-performance electronic products. What makes it better than carbon nanotubes is that when making complex circuits, nanotubes must be carefully screened and positioned.
Silicon-based microcomputer processors can only perform a certain number of operations per second at room temperature. However, electrons pass through graphene with almost no resistance, and the heat generated is very small. In addition, graphene itself is a good thermal conductor and can quickly dissipate heat. Because of their excellent performance, graphene-made electronics run much faster. Relevant experts point out: "The speed of silicon is limited, it can only reach the point where it is now, and it can no longer be improved." The operating speed of silicon devices has reached the range of gigahertz. Computers made of graphene devices can run at terahertz, which is 1,000 times faster than 1 gigahertz.
In addition to making computers run faster, graphene devices can also be used in communications and imaging technologies that require a high-speed operation. Relevant experts believe that graphene is likely to be first applied to high-frequency fields, such as terahertz imaging, and one of its uses is to detect hidden weapons. However, speed is not the only advantage of graphene. Silicon cannot be divided into small pieces smaller than 10 nanometers, otherwise, it will lose attractive electronic properties. Compared with silicon, when graphene is divided into small pieces of nanometers, its basic physical properties do not change.
Research results released
Experiments by a scientific team led by Michael S. Fuhrer, a professor of physics at the Center for Nanotechnology and Advanced Materials at the University of Maryland, have shown that graphene's electron mobility does not change with temperature. They measured the electron mobility of graphene between 50 Kelvin and 500 Kelvin and found that no matter how the temperature changes, the electron mobility is about 150,000 cm2 / Vs. The electron mobility of silicon is 1400 cm2 / Vs. Electrons travel 100 times faster in silicon than silicon, so future semiconductor materials are graphene instead of silicon. This will make it possible to develop faster computer chips and biochemical sensors. They also measured the thermal vibration effect of electron conduction in graphene for the first time. Experimental results show that the thermal vibration effect of electron conduction in graphene is very small.
The calculation results of Liu Fang and Li Ju, a researcher and collaborator of the Academy of Mathematics and Systems Science of the Chinese Academy of Sciences, show that the ideal strength of the predicted graphene is 110GPa ～ 121GPa. This means that graphene is the strongest material known to man.
James Hone and Jeffrey Kysar's group at Columbia University announced in the July 2008 issue of Science that graphene is the most robust material known in the world. They found that before the graphene sample particles began to fragment, the maximum pressure they could withstand every 100 nanometers was about 2.9 micronewtons. This result is equivalent to the pressure of 55 Newtons to break 1-meter long graphene.
If graphene with a thickness equivalent to a plastic packaging bag (thickness of about 100 nanometers) can be made, it will need to apply about 20,000 Newtons of pressure to tear it off. This means that graphene is harder than diamond.
Published in the "Science" magazine on September 26, 2008, Cai Weiwei, a Ph.D. student in the Solid State Quantum Information Laboratory of the Institute of Physics of the Chinese Academy of Sciences, under the guidance of researcher Chen Dongmin and Professor Rodney Ruoff, had successfully made high-quality 13C isotopically synthesized graphite, and 13C-graphite was further dissociated into 13C-graphene and its derivative 13C-graphene oxide. Analysis of this material revealed the long-controversial chemical structure of graphene oxide.
Low noise graphene transistor
In March 2008, scientists at the IBM Watson Research Center took the lead in making low-noise graphene transistors in the world.
As the size of ordinary nano-devices decreases, the noise called 1 / f will become more and more obvious, which will worsen the device's signal-to-noise ratio. This phenomenon is called Hooge's law, and it can occur in graphene, carbon nanotubes, and silicon materials. Therefore, how to reduce the 1 / f noise becomes one of the key issues for implementing nano-devices. IBM successfully trial-produced the transistor by overlapping two layers of graphene. The strong 1 / f noise is controlled by the strong electron bond between the two layers of graphene. The discovery by IBM-Chinese researcher Ming-Yu Lin proves that two-layer graphene is expected to be applied in various fields.
In May 2008, Deshill, a professor at Georgia Institute of Technology in the United States, collaborated with the Massachusetts Institute of Technology's Lincoln Laboratory to generate hundreds of graphene transistor arrays on a single chip.
At the end of June 2008, Professor Mitsuko Maki, Institute of Electrical and Communications Research, Tohoku University, Japan generated a single-layer graphite film, namely graphene, on a silicon substrate. It can achieve high-speed operation of the device without shrinking, for example, it can be used to make 1012 Hz-level high-frequency devices and super microprocessors. A single-layer graphite film is difficult to make and has a honeycomb graphite structure with a thickness of only one carbon atom. Professor Moguang's team controlled the crystalline direction when the silicon carbide was formed and the crystalline direction when the silicon substrate was cut to obtain a two-layer graphite film with an area of 100 × 150 square micrometers. The lattice distortion rate of other scientific research teams using traditional methods is 20%, so they cannot be made into practical devices. Professor Sumitomo's method is to heat the silicon carbide substrate to more than 1,000 degrees under vacuum, remove the remaining carbon from silicon, and form a single-layer graphite film by self-assembly.
Current status of graphene crystals
The 2010 Nobel Prize in Physics, graphene attracted people's attention. In 2004, Professor Andre Heim and Konstantin Novoselov of the University of Manchester in the United Kingdom stripped graphene from graphite flakes in a very simple way, for which they also won the 2010 Nobel Prize award in Physics.
Graphene is a two-dimensional crystal. Carbon atoms are arranged in hexagons and connected to each other to form a carbon molecule. Its structure is very stable. As the number of connected carbon atoms continues to increase, this two-dimensional carbon molecule plane expands, so does the molecule. A single layer of graphene has a thickness of only one carbon atom, that is, 0.335 nanometers, which is equivalent to one 200,000th of the thickness of a hair. There are nearly 1.5 million layers of graphene in 1-mm-thick graphite. Graphene is the thinnest material known and has the advantages of extremely high specific surface area, superconductivity, and strength.
Graphene is the thinnest material currently known. A single layer of graphene has a thickness of only one carbon atom, and this thickness of graphene has many characteristics not available in graphite.
Extremely conductive: The electrons in graphene have no mass, and the speed of electrons exceeds the speed of movement in other metal monomers or semiconductors, which can reach 1/300 of the speed of light. Because of this, graphene has a super-strong conductivity.
Ultra-high strength: Graphite is the softest of minerals. Its Mohs hardness is only 1-2. After being separated into graphene with a thickness of carbon atoms, its performance will change suddenly. Its hardness will be higher than the diamond whose hardness is 10 grade.
Large specific surface area: Because the thickness of graphene is only one carbon atom, that is, 0.335 nanometers, graphene has a large specific surface area. The specific surface area of ideal single-layer graphene can reach 2630m2 / g, while the specific surface area of ordinary activated carbon is 1500m2 / g. The large specific surface area makes graphene a potential energy storage material.
The main producing methods include micromechanical peeling, epitaxial growth, graphite oxide reduction, and vapor deposition. Among them, the graphite oxide reduction method is at a relatively low cost and is the main method.
Graphene's good electrical conductivity and light transmission properties make it a very good application prospect for transparent conductive electrodes. Touch screens, liquid crystal displays, organic photovoltaic cells, organic light-emitting diodes are products that need good transparent conductive electrode materials. In particular, graphene has better mechanical strength and flexibility than the commonly used material indium tin oxide. Graphene films in a solution can be deposited over large areas. By chemical vapor deposition, large-area, continuous, transparent, high-conductivity, few-layer graphene films can be made. It is mainly used for the anode of photovoltaic devices and achieves an energy conversion efficiency of up to 1.71%. Compared with the fabricated element, its energy conversion efficiency is about 55.2%. As an emerging industry. The future of graphene is bright.
Graphene's special structure makes it the hardest and thinnest in the world, and it also has strong toughness, electrical conductivity, and thermal conductivity. These and its special characteristics make it have tremendous development space, and it can be applied to a large number of fields such as electronics, aerospace, optics, energy storage, biomedicine, daily life, and so on.
Frequently Asked Questions
A graphene field effect transistor (GFET) is composed of a graphene channel between two electrodes with a gate contact to modulate the electronic response of the channel (Figure 1). The graphene is exposed to enable functionalization of the channel surface and binding of receptor molecules to the channel surface.
Graphene field-effect transistors (GFETs) are emerging as bioanalytical sensors, in which their responsive electrical conductance is used to perform quantitative analyses of biologically-relevant molecules such as DNA, proteins, ions and small molecules.
Graphene has many properties (in all forms) that make it an ideal material for electronic devices, ranging from its superior electrical conductivity properties to its high charge carrier mobility and its large and active surface area. Unlike silicon, graphene does not have a bandgap, making it highly conductive.
Essentially, graphene is a 2D sheet made of carbon atoms that has incredible properties of tensile strength and conductivity making it the thinnest yet the strongest martial. It conducts heat better than any other material and is also an excellent semi-conductor, making it a great material for computers.
If too much of the current is lost in the transistor, there will be loss instead of gain, and the device will be useless. Graphene FETs tend to have rather poor output resistance when the gate lengths are small, so this problem is serious for graphene.