The singular properties of nanomaterials include:

①Surface effect

  The surface area of a spherical particle is proportional to the square of the diameter, and its volume is proportional to the cube of the diameter, so its specific surface area (surface area/volume) is inversely proportional to the diameter. As the particle diameter becomes smaller, the specific surface area will increase significantly, indicating that the percentage of surface atoms will increase significantly. If the interatomic distance is 3'10-4 microns, the surface atoms will only occupy one layer, a rough estimate of the surface See the table below for the percentage of atoms.
   The relationship between surface atomic percentage of ultrafine particles and particle diameter
Diameter ('10-4 microns)  10   50    100    1000
Total number of protons 30 4′ 103 3′ 104 3′  106

Percent surface protons  100   40    20     2

It can be seen from the above table that the surface effect on particles with a diameter greater than 0.1 micron is negligible. When the size is less than 0.1 micron, the surface atomic percentage increases drastically, and the total surface area of 1 gram of ultrafine particles can even be as high as 100 m2. The surface effect at this time cannot be ignored. The surface of ultra-fine particles is very different from the surface of large objects. If a high-magnification electron microscope is used to take a video of gold ultra-fine particles (2'10-3 microns in diameter), the real-time observation reveals that these particles have no fixed shape. , As time changes, it will automatically form various shapes (such as cubic octahedron, decahedron, icosahedral poly Lijing, etc.), it is not only different from ordinary solids, but also different from liquids, it is a kind of quasi-solid. Under the electron beam irradiation of the electron microscope, the surface atoms seem to have entered a "boiling" state, and the instability of the particle structure cannot be seen after the size is greater than 10 nanometers. At this time, the microparticles have a stable structure state.
  The surface of ultrafine particles has high activity, and metal particles in the air will rapidly oxidize and burn. If you want to prevent spontaneous combustion, you can use surface coating or consciously control the oxidation rate to slowly oxidize to form a very thin and dense oxide layer to ensure surface stability. Utilizing surface activity, metal ultrafine particles are expected to become a new generation of high-efficiency catalysts, gas storage materials and low melting point materials.

②Small size effect

  As the particle size changes, under certain conditions, it will cause a qualitative change in the nature of the particles. The change in macroscopic physical properties caused by the smaller particle size is called the small size effect. For ultrafine particles, the size becomes smaller and the specific surface area also increases significantly, resulting in a series of novel properties as follows.
(1) Special optical properties
  When gold is subdivided into a size smaller than the wavelength of light, it loses its original rich luster and appears black. In fact, all metals appear black in the state of ultrafine particles. The smaller the size, the darker the color, silver-white platinum (white gold) becomes platinum black, and metallic chromium becomes chrome black. It can be seen that the reflectivity of metal ultrafine particles to light is very low, usually less than 1%, and the thickness of about a few microns can be completely extinct. Using this feature, it can be used as a high-efficiency conversion material such as photothermal and photovoltaics, and can efficiently convert solar energy into thermal energy and electrical energy. In addition, it may be applied to infrared sensitive components, infrared stealth technology, etc.
(2) Special thermal properties
  The melting point of solid matter is fixed when its shape is large, but it is found that its melting point will be significantly reduced after ultra-micronization, especially when the particles are smaller than 10 nanometers. For example, the conventional melting point of gold is 1064C. When the particle size is reduced to 10 nanometers, it decreases by 27°C, and the melting point at 2 nanometers is only about 327C; the conventional melting point of silver is 670C, while the melting point of ultrafine silver particles Can be lower than 100°C. Therefore, the conductive paste made of ultra-fine silver powder can be sintered at low temperature. In this case, the substrate of the element does not need to use high-temperature resistant ceramic materials, and even plastics can be used. The use of ultra-fine silver powder paste can make the film thickness uniform, cover a large area, save materials and have high quality. Japan’s Kawasaki Steel Corporation uses 0.1 to 1 micron copper and nickel ultrafine particles to make conductive pastes that can replace precious metals such as palladium and silver. The reduced melting point of ultrafine particles is attractive to the powder metallurgy industry. For example, adding 0.1% to 0.5% by weight of ultrafine nickel particles to tungsten particles can reduce the sintering temperature from 3000°C to 1200 to 1300°C, so that high-power semiconductor tubes can be fired at a lower temperature.
(3) Special magnetic properties
  People have discovered that there are ultra-fine magnetic particles in organisms such as pigeons, dolphins, butterflies, bees, and magnetotactic bacteria living in the water, so that these organisms can distinguish directions under the geomagnetic field navigation and have the ability to return. Magnetic nanoparticles are essentially a biological magnetic compass. Magnetotactic bacteria living in water rely on it to swim to the nutrient-rich bottom. Studies by electron microscopy have shown that magnetotactic bacteria usually contain magnetic oxide particles with a diameter of about 2'10-2 microns. The magnetic properties of small-size ultrafine particles are significantly different from those of bulk materials. The coercivity of bulk pure iron is about 80 A/m. When the particle size is reduced to below 2′10-2 microns, its coercivity It can be increased by a thousand times. If the size is further reduced, when the size is less than 6'10-3 microns, the coercive force will decrease to zero instead, showing superparamagnetism. Utilizing the characteristics of high coercivity of magnetic ultrafine particles, it has been made into magnetic recording magnetic powder with high storage density, which is widely used in magnetic tapes, magnetic disks, magnetic cards and magnetic keys. Using superparamagnetism, people have made magnetic ultrafine particles into magnetic liquids with a wide range of uses.
(4) Special mechanical properties
  Ceramic materials are brittle under normal circumstances, but nano-ceramic materials made of nano-ultrafine particles have good toughness. Because nanomaterials have a large interface, the atomic arrangement of the interface is quite chaotic. Atoms can easily migrate under the condition of external force and deformation. Therefore, they exhibit very good toughness and a certain degree of ductility, making ceramic materials have novel mechanical properties. American scholars reported that calcium fluoride nanomaterials can be bent largely without breaking at room temperature. Studies have shown that the reason why human teeth have high strength is because they are made of nano-materials such as calcium phosphate. Nano-grained metals are 3 to 5 times harder than traditional coarse-grained metals. As for composite nano-materials such as metal-ceramics, the mechanical properties of materials can be changed in a larger range, and their application prospects are very broad.
  The small size effect of ultrafine particles is also manifested in superconductivity, dielectric properties, acoustic properties and chemical properties.

③ Macroscopic quantum tunneling effect

  Atoms of various elements have specific spectral lines, such as sodium atoms have yellow spectral lines. Atomic models and quantum mechanics have used the concept of energy levels for a reasonable explanation. When a solid is composed of countless atoms, the energy levels of individual atoms are combined into energy bands. Due to the large number of electrons, the distance between energy levels in the energy band is very small. Therefore, it can be regarded as continuous, and successfully explained the connection and difference between bulk metals, semiconductors, and insulators from the energy band theory. For ultrafine particles between atoms, molecules and bulk solids , The continuous energy bands in the bulk material will split into discrete energy levels; the distance between the energy levels increases as the particle size decreases. When thermal energy, electric field energy or magnetic field energy is smaller than the average energy level spacing, it will show a series of abnormal characteristics that are completely different from macroscopic objects, which is called quantum size effect. For example, conductive metals can become insulators in ultrafine particles. The magnitude of the magnetic moment is related to whether the electrons in the particles are odd or even. The specific heat will also change abnormally, and the spectral lines will move to the short-wavelength direction. This is quantum The macroscopic performance of the size effect. Therefore, quantum effects must be considered for ultrafine particles under low temperature conditions, and the original macroscopic laws are no longer valid.
  Electrons have both particle and volatility, so there is a tunneling effect. In recent years, it has been discovered that some macroscopic physical quantities, such as the magnetization of micro-particles and the magnetic flux in quantum coherent devices, also exhibit tunneling effects, which are called macroscopic quantum tunneling effects. Quantum size effect and macroscopic quantum tunneling effect will be the basis of future microelectronics and optoelectronic devices, or it will establish the limit of further miniaturization of existing microelectronic devices. When microelectronic devices are further miniaturized, the aforementioned quantum effects must be considered. For example, in the manufacture of semiconductor integrated circuits, when the size of the circuit is close to the wavelength of electrons, electrons overflow the device through the tunneling effect, making the device unable to work normally. The limit size of the classic circuit is about 0.25 microns. The quantum resonance tunneling transistor developed at present is a new generation device made by quantum effect.