1990, scientists from the International Business Machines Corporation of the United States used a probe on a tunneling scanning microscope to discharge the letter "IBM" with 36 xenon atoms on the surface of nickel. Scientists see the hope of designing and manufacturing molecular-sized devices from this nanotechnology, which can manipulate a single atom. 1993, China academy of sciences Beijing vacuum physics laboratory manipulated atoms and successfully wrote the word "China", which marked that China began to occupy a place in the international nanotechnology field.
Since 1990s, the development of quasi-one-dimensional nanomaterials has been the frontier of nanotechnology. 199 1 year 1 month, S. Iijima of NEC Laboratory in Tsukuba, Japan observed carbon nanotubes for the first time with high-resolution analytical electron microscope. These carbon nanotubes are multilayer coaxial tubes, also known as bucky tubes. In June 2000, 5438+ 10, researchers from the University of Pennsylvania published an article in Science magazine, saying that the mass of carbon nanotubes is one sixth of that of steel with the same volume, but its strength is 100 times higher than that of steel. It has not only good electrical conductivity, but also the best thermal conductivity material at present. The excellent thermal conductivity of carbon nanotubes makes them a heat sink for future computer chips, and can also be used as protective materials for various high-temperature components such as engines and rockets. The latest research shows that the cavity in carbon nanotubes can not only be used as a miniature test tube, mold or template, but also can seal the second substance in this limited space and induce it to have a structure and behavior that can't be seen in macro materials. Computer simulation shows that water sealed in carbon nanotubes can exist as a new ice phase. Under suitable conditions, the obvious boundary between liquid phase and solid phase in carbon nanotubes will disappear, and liquid substances will continue to transform into solid state without obvious solidification process.
In 1993, Bethune et al. of almaden Laboratory of IBM and Iijima simultaneously reported the observation results of single-walled carbon nanotubes. 1996, Smali, who won the Nobel Prize for discovering C60, and his research combined to form single-walled carbon nanotube bundles arranged in rows. In the same year, researcher Xie of Institute of Physics, Chinese Academy of Sciences prepared a large-area carbon nanotube array with an area of 3mm×3mm by chemical vapor method, which can be used as an excellent field emission flat panel display device. They also synthesized fiber-grade carbon nanotubes with the longest length of 2 mm at 1998.
In addition to carbon nanotubes, researchers also synthesized other nanotube materials, such as BxCyNz, NiCl2, ester-like body, MCM-4 1 pipe-in-pipe, diaspore, b-(g-) cyclodextrin nanotube aggregates and aligned silicon nitride nanotubes [1]. Besides hollow nanotubes, there are solid nanorods, nanowires and quantum wires in quasi-one-dimensional nanomaterials. Figure 1 shows the silica nanowire assembled by our research, with a diameter of 5- 120nm and a length of 10-70mm from the tip to the root. 1997, French scholar Colliex obtained a kind of C-BN-C tube coated with heterogeneous nano-shell by analyzing arc discharge. Because its geometric structure is similar to coaxial cable and its diameter is nanometer, it is called coaxial nano-cable. Coaxial nano-cables will play an important role in nano-structured devices due to their unique structures.
From 65438 to 0996, Dr. Xie Yi of China University of Science and Technology prepared gallium nitride powder with high yield and average particle size of 30nm by benzene thermal synthesis. From 65438 to 0997, Professor Fan Shoushan of Tsinghua University prepared gallium nitride nanorods with a diameter of 3-50 nanometers and a length of micron, and prepared gallium nitride into one-dimensional nanocrystals for the first time, and put forward the concept of carbon nanotubes limiting reaction. 65438-0999 cooperated with Professor Dai Hongjie of Stanford University to realize the self-organized growth of carbon nanotube arrays on silicon substrates.
1997, scientists from new york University found that DNA (deoxyribonucleic acid) can be used to build nano-scale mechanical devices. In 2000, scientists from Lucent Company of the United States and Oxford University of the United Kingdom made use of the base pairing mechanism of DNA to create a nano-sized tweezers, each arm being only 7 nanometers long.
From 65438 to 0998, the research group of Academician Qian Yitai of China University of Science and Technology used carbon tetrachloride as raw material to prepare diamond nano-powder, which was praised as "turning stone into gold" by international publications.
From 65438 to 0999, the research group of Professor Xue Zengquan of Peking University Department of Electronics assembled single-walled carbon nanotubes on the metal surface and assembled probes with good performance for scanning tunneling microscope. In the same year, Dr. Cheng Huiming from Institute of Metals, Chinese Academy of Sciences synthesized high-quality carbon nanomaterials, which made the research on new hydrogen storage materials in China leap to the advanced level in the world.
1999, Brazilian and American scientists made the world's smallest "scale" with carbon nanotubes, and its weight can reach one billionth of a gram, which is equivalent to the weight of a virus. Soon, German scientists developed a "nano-scale" to weigh a single atom, breaking the previous record. In the same year, American scientists realized an organic switch on a single molecule, which proved that electronic and computing devices can be developed at the molecular level.
Lu Ke's research group of Shenyang Institute of Metals, China Academy of Sciences has made outstanding achievements in the field of nano-materials and related metastable materials. The method he developed to prepare dense nano-alloy by amorphous complete crystallization, together with in-situ pressure after evaporation of inert gas and high-energy ball milling, has become one of the three main methods to prepare metal nano-blocks. They found that the superplastic ductility of nano-copper at room temperature was rated as the top ten science and technology news in China in 2000.
Since the discovery of carbon nanotubes, scientists have been developing thinner and thinner carbon nanotubes. In 2000, Xie's team prepared carbon nanotubes with an inner diameter of 0.5 nm by the usual arc discharge method. In the same year, Dr. Tang Zikang of the Hong Kong University of Science and Technology announced the discovery of the world's finest pure carbon nanotubes? 0.4nm carbon nanotubes, this result has reached the theoretical limit of carbon nanotubes. Thin-walled nanotubes with a diameter of 1nm were developed by Max-Born Institute in Berlin in February, 65438, which set a new record for the development of thin-walled nanotubes.
At the beginning of 200 1, the research group of Academician Zhu Qingshi of China University of Science and Technology directly photographed C60 single molecule image which can distinguish chemical bonds for the first time. This single-molecule direct imaging technology provides an effective means for analyzing the internal structure of molecules, enabling scientists to manually "cut" and "recombine" chemical bonds, laying the foundation for designing and preparing single-molecule nano-devices. In March, the research team of Professor Wang Zhonglin, a China scholar at Georgia Institute of Technology, USA, synthesized a unique and defect-free semiconductor oxide nanobelt structure for the first time in the world by high-temperature solid-gas phase method. This is a new member of the nano-family after nanotubes and nanowires. It is expected to solve the stability problem of nanotubes in large-scale production and play an important role in nano-physics research and nano-device application. In June, the research team of Professor Shen Ping from Hong Kong University of Science and Technology observed superconductivity in a single pure carbon nanotube. This observation shows that when carbon nanotubes are fine to a certain extent, their material properties will change suddenly. In application, the discovery of superconductivity of carbon nanotubes will help solve the problem of heat generation when electrons are transmitted in integrated semiconductor devices.
As can be seen from the above, China is not backward in the field of nano-basic research? Since the early 1990s, the Ministry of Science and Technology, the National Natural Science Foundation of China, the Chinese Academy of Sciences and other units have started the climbing plan of nano-materials and national key basic research projects, and invested tens of millions of yuan to support nano-basic research. Nanoscientists in China have made a series of remarkable achievements in the world, and published high-level papers in authoritative magazines such as Science and Nature, which makes China in a relatively leading position in the basic research of nanomaterials, especially in the controllable synthesis of nanostructures, ranking fourth in the world after the United States, Japan and Germany. But generally speaking, the research level of nano-devices is not very high, and there is still a big gap between the means and foreign countries.
Second, the application of nanotechnology.
In nano-materials, the periodic boundary conditions of crystals are destroyed because the size of nano-scale is equal to or smaller than the physical characteristic sizes such as wavelength of light wave, de Broglie wavelength and coherence length of superconducting state. The atomic density near the surface of nanoparticles decreases; The average free path of electrons is very short, but the localization and coherence are enhanced. The reduction of size also greatly reduces the number of atoms contained in the nano-system, and the macroscopic fixed quasi-continuous energy band is transformed into discrete energy levels. These physical effects lead to macroscopic acoustic, optical, electrical, magnetic, thermal and mechanical effects of nano-materials, which are different from conventional materials, such as quantum size effect, small size effect, surface effect and macroscopic tunneling effect. At present, the description of basic physical effects in nano-materials is mainly developed and established on the basis of the study of metal nanoparticles. In order to accurately grasp the essence of phenomena in nanotechnology, it is necessary to realize the transformation from continuous system physics to quantum physics in theory.
Nowadays, the development of science and technology requires ultra-miniaturization, intelligence, high integration of components, high-density storage and ultra-high-speed transmission, which provides a broad space for the application of nanotechnology and nano-materials. The fields of nanotechnology listed in the National Nanotechnology Initiative (NNI) formulated by the United States are very extensive, but there are three basic fields, namely nanomaterials, nanoelectronics, optoelectronics and magnetism, nanomedicine and biology.
1 nanoelectronics, optoelectronics and magnetism
The macroscopic tunneling effect of nanoparticles limits the miniaturization of microelectronic devices. For silicon integrated circuits, the limit linewidth of microelectronic devices in nanoelectronics, optoelectronics and magnetism is generally considered to be about 70nm. At present, the world's narrowest linewidth 130nm will reach its limit within ten years. If the silicon device is made smaller, electrons will tunnel through the insulating layer, resulting in a short circuit. At present, there are two ways to solve nano-electronic circuits. One method is to use the quantum entangled state in the two-photon beam technology in the integrated circuit manufactured by lithography, which may reduce the limit of the device to 25 nanometers. The other is to develop new materials to replace silicon, using protein diodes and carbon nanotubes as wires and molecular wires. Single atom manipulation is an important way to form new concept devices. 1997, American scientists successfully moved a single electron with a single electron. This technology can be used to develop quantum computers whose speed and storage capacity are 10 thousand times higher than now. In July, 200 1 year, Dutch researchers manufactured a single-electron carbon nanotube transistor, which can work effectively at room temperature. This transistor is based on carbon nanotubes and relies on an electron to determine the "on" and "off" states. Because of its low energy consumption, it will become an ideal material for molecular computers. In the new century, superconducting quantum coherent devices, ultra-micro Hall detectors and ultra-micro magnetic field detectors will become the protagonists of devices in nanoelectronics.
The reading head developed by using the phenomenons of giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) in nanomagnetism can increase the recording density of the magnetic disk by more than 30 times. Researchers in Zurich, Switzerland, prepared nanowires alternately filled with copper and cobalt, and used their giant magnetoresistance to prepare ultramicro magnetic field sensors. Magnetic nanoparticles have small particle size, single domain structure and high coercivity, so they can be used as magnetic recording materials to improve signal-to-noise ratio and image quality. During the period of 1997, the nanostructured disk was successfully developed by the nanostructured laboratory of the Department of Electronic Engineering, University of Minnesota. The Co rods with a length of 40 nm were arranged in a periodic quantum rod array. Because nano-magnetic units are separated from each other, they are called quantum disks. It uses the storage characteristics of magnetic nanowire arrays, and the storage density can reach 400Gb×in-2. Magnetic sensors prepared by giant magneto-impedance effect of iron-based nanomaterials have come out, and magnetic liquids coated with superparamagnetic nanoparticles are also widely used in aerospace and some civil fields as long-life dynamic rotary seals.
2 nm medicine and biology
From protein, DNA, RNA to viruses, they are all within the scale of 1- 100nm, so nanostructures are also the basic things in life phenomena. Organels and other structural units in cells are "nano-machines" that perform certain functions. Cells are like "nano-workshops", and photosynthesis in plants is a typical example of "nano-factories". The self-assembly arrangement of genetic gene sequences realizes the accurate structure at atomic level, and the information transmission and feedback of nervous system is a perfect example of nanotechnology. Biosynthesis and biological processes have become the source of inspiration and manufacture of new nanostructures, and researchers are imitating biological characteristics to realize the control and manipulation of technology at the nanometer scale.
The size of nanoparticles is often smaller than cells and red blood cells in organisms, which provides a new opportunity for medical research. At present, examples that have been well applied include: cell separation technology using nano-silica particles, intracellular staining of nanoparticles, especially gold (Au) particles, and local targeted therapy with new drugs or antibodies coated with magnetic nanoparticles.
Biochips under development include cell chip, protein chip (biomolecule chip) and gene chip (DNA chip), which have the advantages of integration, parallelism and rapid detection, and have become the frontier technology of nano-bioengineering. It will be directly applied to clinical diagnosis, drug development and human gene diagnosis. After being implanted into the human body, people can enjoy medical treatment anytime and anywhere, and find the premonitory information of diseases in dynamic detection, which makes early diagnosis and prevention possible.
Nano-biomaterials can also be divided into two categories. One is nano-materials suitable for life, such as various nano-sensors, which are used for early diagnosis, monitoring and treatment of diseases. Various nano-mechanical systems can quickly identify the location of the ward, inject drugs into the ward directionally without damaging normal tissues or removing cardiovascular and cerebrovascular thrombosis and fat deposition, and even use them to devour viruses and kill cancer cells. The other is nano-materials developed by using the activity of biomolecules, which can replace organisms for other nano-technologies or micro-processing.
Application of 3 in national defense science and technology
Nanotechnology will bring revolutionary influence to national defense and military field. For example, nano-electronic equipment will be used for real-time communication between virtual training system and battlefield; Nano-detection system for chemical, biological and nuclear weapons; New nano-materials can improve the strike and protection ability of conventional weapons; Small robots made of nano-micro mechanical systems can complete special reconnaissance and strike tasks; Nanosatellites can be launched by small launch vehicles and form satellite networks according to different orbits to monitor every corner of the earth and make the battlefield more transparent. The application of nano-materials in stealth technology is particularly noticeable.
In radar stealth technology, the preparation of ultra-high frequency (SHF, GHz) electromagnetic wave absorbing materials is the key. Nanomaterials are being developed as a new generation of stealth materials. Due to the large proportion of interface components in nano-materials, the proportion of atoms on the surface of nano-particles is high, and the number of unsaturated bonds and dangling bonds increases. The existence of a large number of dangling bonds polarizes the interface and broadens the absorption band. High specific surface area leads to multiple scattering. The quantum size effect of nano-materials makes the energy levels of electrons split, and the split energy levels are within the energy range of microwave, which creates a new absorption channel for nano-materials. Under the irradiation of microwave field, the motion of atoms and electrons in nano-materials is intensified, which increases the efficiency of converting electromagnetic energy into heat energy, thus improving the absorption performance of electromagnetic waves. The absorption rate of "ultra-black powder" nano-absorbing material developed in the United States reaches 99%, and the nano-composite material coated with insulating layer by CoNi nanoparticles recently developed in France has m? And m are almost all greater than 6. Recently, foreign countries are trying to study nanocomposites covering centimeter wave, millimeter wave, infrared and visible light, and put forward a single absorption particle matching design mechanism, which can give full play to the role of unit mass loss layer. Nano-materials have good absorbing function, but they are generally thin, light, wide and strong. Borides, carbides and ferrites in nano-materials (including nanofibers and carbon nanotubes) will have great potential in the application of stealth materials.
Fig. 2 is a transmission electron microscope photograph of b- nano silicon carbide powder prepared by our research group by sol-gel method. The primary particle size is about 20nm. The dielectric loss (tgd) measured by microwave network vector analyzer is 9.28, while the dielectric loss of other silicon carbide powders is between 0.2 and 0.6, so it has the potential to absorb UHF electromagnetic waves at room temperature and high temperature.
Strengthening and toughening of 4 nano-ceramics
Advanced ceramic materials play an irreplaceable role in harsh environments such as high temperature and strong corrosion. However, brittleness is an insurmountable weakness of ceramic materials. Cahn, a British material scientist, once commented that the attempt to overcome the brittleness of ceramics by improving the process and chemical composition is not ideal, and neither solid solution doped silicon nitride nor phase change toughened zirconia can be used as ceramic engine materials in practice. Nano-ceramics is one of the strategic ways to solve the brittleness of ceramics.
The superplasticity of nano-ceramics similar to that of metals is the focus of attention in the research of nano-materials. For example, nano calcium fluoride and nano titanium oxide ceramics can undergo plastic deformation at room temperature, and the plastic deformation can reach 100% at 180℃. When the prefabricated crack specimen is bent at 180℃, the crack will not propagate. In the early 1990s, Niihara in Japan reported that the strength of alumina composites with nano-SiC particles can reach above 1 GPA, while the strength of conventional alumina-based ceramics is only 350-600MPa. The strength of Al2O3/SiC nanocomposites is increased to 65438±0.5 GPA after annealing in argon at 65438 0300℃ for 2 hours, and its high mechanical properties are directly related to the fine microstructure of nanocomposites. A-Si3N4 microcrystals and a-SiC nanocrystals were prepared by researchers from Max Planck Institute of Metallurgical Materials in Germany after pyrolysis of polymethylsilazane at high temperature. It has good high-temperature oxidation resistance and can be used at the high temperature of 1600℃ (the highest use temperature of silicon nitride material is generally 1200- 1300℃). Their latest progress is to improve the thermal stability of the material by adding boride, stabilize the nano-silicon nitride grains by the coating effect of the generated BN, and further increase the service temperature of this Si-B-C-N ceramic to 2000℃, which is the highest temperature bulk ceramic material in the world so far.
At present, the preparation of nano-ceramic powder is relatively mature, and new technologies and methods are constantly emerging, which has reached the production scale. The preparation methods of nano-ceramic powder mainly include gas phase method, liquid phase method and high energy ball milling method. Gas phase method includes inert gas condensation method, plasma method, gas pyrolysis method, electron beam evaporation method and so on. Liquid phase methods include chemical precipitation, alcoholysis, sol-gel method, hydrothermal method and so on. Our research group proposed to prepare nanocrystalline TiC and TiN composite TZP powder by in-situ selective reaction, which provided a new research idea for the microstructure design of ceramic materials. Densification methods of nano-ceramics tend to be diversified, among which microwave sintering and spark plasma sintering have better effects. Professor Chen Yiwei of the University of Pennsylvania in the United States prepared dense Y2O3 bulk materials with an average particle size of 60nm by pressureless sintering, which brought new hope for the development of nano-ceramics. In June, 20001year, Japan's Ministry of Economy, Trade and Industry reported that new materials such as nano-ceramics were applied to aircraft parts manufacturing technology.
Application of 5 nanometer technology in other fields
The excellent properties of nanoparticles, such as large specific surface area, high surface reactivity, many surface active centers, high catalytic efficiency and strong adsorption capacity, make them have important applications in chemical catalysis. Nano-powders such as platinum black, silver, alumina and iron oxide have been directly used as catalysts for oxidation, reduction and synthesis of polymers, which greatly improves the reaction efficiency. The combustion efficiency of rocket solid fuel with nano-nickel powder as reaction catalyst can be increased by 100 times. When the particle size of nickel is below 5nm, the reaction selectivity changes dramatically, the aldehyde decomposition reaction is effectively controlled, and the conversion rate of alcohol increases rapidly.
Miniaturization itself does not represent nanotechnology. Nanomaterials and nanotechnology are clearly defined in terms of scale and performance. At present, the main method of manufacturing nano-devices is to reduce the dimension of material structure from top to bottom, and the future development direction of nano-technology is to build nano-devices from bottom to top. At present, there are two kinds of attempts in this regard. One is the artificial realization of single atom manipulation and molecular surgery. Researchers at Osaka University in Japan synthesized three-dimensional nano-cows and nano-springs in polymer materials by using two-photon absorption technology, which made a new breakthrough in the preparation and acceptance of functional micro-devices. The other is the molecular self-assembly technology of various systems. Nanostructures constructed by molecular self-assembly include nanorods, nanotubes, multilayer films, pore structures and so on. Scientists at Bell Laboratories have prepared a single-layer field effect transistor with a diameter of 1-2nm by using the self-assembly technology of organic molecule mercaptan. The preparation of this single-layer nano-transistor is an important step in developing molecular electronic devices. The work in this field is still limited to the laboratory research stage.