球形颗粒的表面积与直径的平方成正比，其体积与直径的立方成正比，故其比表面积(表面积/体积)与直径成反比。随着颗粒直径变小，比表面积将会显著增大，说明表面原子所占的百分数将会显著增加。对直径大于0.1μm的颗粒的表面效应可忽略不计，当尺寸小于0.1μm时，其表面原子百分数急剧增长，甚至1g超微颗粒表面积的总和可高达l00m2，这时的表面效应将不容忽略。超微颗粒的表面与大块物体的表面是十分不同的，若用高倍率电子显微镜对金超微颗粒(直径为2×10-3μm)进行电视摄像，实时观察发现这些颗粒没有固定的形态，随着时间的变化会自动形成各种形状(如立方八面体，十面体，二十面体多粒晶等)，它既不同于一般固体，又不同于液体，是一种准固体。在电子显微镜的电子束照射下，表面原子仿佛进入了“沸腾”状态，尺寸大于10nm后才观察不到这种颗粒结构的不稳定性，这时微颗粒具有稳定的结构状态。超微颗粒的表面具有很高的活性，在空气中金属颗粒会迅速氧化且燃烧。如要防止自燃，可采用表面包覆或有意识地控制氧化速率，使其缓慢氧化生成一层极薄且致密的氧化层，确保表面稳定化。利用表面活性，金属超微颗粒有望成为新一代的高效催化剂、储气材料或低熔点材料。
当纳米粒子的尺寸与光波的波长、传导电子的德布罗意波长以及超导态的相干长度或透射深度等物理尺寸相当或比它们更小时，周期性的边界条件被破坏，声、光、电、磁、热力学特性等均会随着粒子尺寸的减小发生显著的变化。这种因尺寸的减小而导致的变化称为小尺寸效应，也叫体积效应。如纳米粒子的熔点可远低于块状固体，此特性为粉末冶金工业提供了新工艺；利用等离子共振频移随颗粒尺寸变化的性质，可以通过改变颗粒尺寸，控制吸收边的位移，构造具有一定频宽的微波吸收纳米材料，用于电磁波屏蔽、隐形飞机等。材料的硬度和强度随着晶粒尺寸的减小而增大，不少纳米陶瓷材料的硬度和强度比普通材料高4—5倍，如纳米TiO2的显微硬度为12.75kPa，而普通TiO2陶瓷的显微硬度低于1.96kPa。在陶瓷基体中引入纳米分散相并进行复合，不仅可大幅度提高其断裂强度和断裂韧性，明显改善其耐高温性能，而且也能提高材料的硬度、弹性模量和抗热震、抗高温蠕变等性能。
纳米材料的量子尺寸效应是指当粒子尺寸达到与光波波长或其他相干波长等物理特征尺寸相当或更小时，金属费米能级附近的电子能级由准连续变为离散，并使能隙变宽的现象。当能级间距δ大于热能、磁能、静磁能、静电能光子能量或超导态的凝聚能时，必须考虑量子效应。由此导致的纳米微粒在催化、电磁、光学、热学和超导等微观特性和宏观性质表现出与宏观块体材料显著不同的特点。例如，纳米银与普通银的性质完全不同，普通银为良导体，而纳米银在粒径小于20nm时却是绝缘体。同样，纳米材料的这一性质也可用于解释为什么SiO2从绝缘体变为导体。
电子具有粒子性又具有波动性，因此存在隧道效应。近年来，人们发现一些宏观物理量，如微颗粒的磁化强度、量子相干器件中的磁通量等亦显示出隧道效应，称之为宏观的量子隧道效应。量子尺寸效应、宏观量子隧道效应将会是未来微电子、光电子器件的基础，或者它确立了现存微电子器件进一步微型化的极限，当微电子器件进一步微型化时必须要考虑上述的量子效应。例如，在制造半导体集成电路时，当电路的尺寸接近电子波长时，电子就通过隧道效应而溢出器件，使器件无法正常工作，经典电路的极限尺寸大概在微米级。目前研制的量子共振隧穿晶体管就是利用量子效应制成的新一代器件。
Characterization of nanomaterials
1: surface and interface effect
The surface area of the spherical particle is proportional to the square of the diameter, and its volume is proportional to the cube of the diameter, so the surface area (surface area / volume) is inversely proportional to the diameter. As the particle diameter becomes smaller, the specific surface area will be significantly increased, indicating that the percentage of the surface atoms will increase significantly. The surface effect of the particles with diameter greater than 0.1 u m will be significantly increased. It should be negligible. When the size is less than 0.1 M, the percentage of the surface atoms increases sharply, even the total surface area of 1G can be as high as l00m2. The surface effect will not be ignored. The surface of the ultramicro particle is very different from the surface of the bulk object. If the gold ultrafine particle is 2 x 10- with the high rate electron microscope, the surface effect of the ultrafine particles is very different. 3 mu m) video camera, real-time observation found that the particles have no fixed shape, with the change of time will automatically form a variety of shapes (such as cubic eight sides, ten sides, twenty planes and so on), it is different from the general solid, but also different from the liquid, is a quasi solid. Under the electron beam electron beam of electron microscope, surface atom It seems to be in the "boiling" state, when the size is greater than 10nm, the instability of the particle structure is not observed, when the microparticles have a stable structural state. The surface of the ultramicro particles is highly active, and the metal particles will oxidize and burn rapidly in the air. To prevent spontaneous combustion, surface coating or conscious control can be used. The oxidation rate makes it slow to oxidize to a thin and dense layer of oxidation to ensure the surface stabilization. By using surface activity, metal ultrafine particles are expected to become a new generation of high efficient catalysts, gas storage materials or low melting point materials.
2: small size effect
When the size of the nanoparticles and the wavelength of the light wave, the De Broglie wavelength of the conductive electron and the coherent length or the transmission depth of the superconducting state are equivalent or smaller than that of them, the periodic boundary conditions are destroyed, and the sound, light, electricity, magnetic, thermodynamic properties and so on will vary significantly with the decrease of the particle size. The small size effect, which is called the small size effect, is called the small size effect, also called the volume effect. For example, the melting point of the nanoparticles is far lower than the bulk solid. This property provides a new process for the powder metallurgy industry. By changing the particle size, the displacement of the absorption edge can be controlled by the change of the particle size by the plasma resonance frequency shift. The hardness and strength of the materials are increased with the decrease of grain size, and the hardness and strength of many nanomaterials are 4 to 5 times higher than that of ordinary materials, such as the microhardness of nano TiO2 is 12.75kPa, and the microhardness of ordinary TiO2 ceramics is lower than that of 1.96kPa.. The introduction of nano dispersive phase and composite in ceramic matrix can not only greatly improve the fracture strength and fracture toughness, but also improve its high temperature resistance, but also improve the hardness, modulus of elasticity, thermal shock resistance and high temperature creep resistance.
3: quantum size effect
The quantum size effect of nanomaterials is the phenomenon that the electron energy level near the metal Fermi level becomes discrete and widens the energy gap when the size of the particle is equal to the wavelength of the light wave or other coherent wavelengths, and the energy gap becomes wider. The quantum effect must be considered when the condensation energy of superconducting states is considered. The resulting nanoparticles show distinct characteristics different from macroscopic bulk materials in the microcosmic and macroscopic properties of catalysis, electromagnetic, optics, heat and superconductivity. For example, the properties of nano silver and ordinary silver are completely different, ordinary silver is a good conductor, and nano silver is less than 20 in particle size. Nm is an insulator. Similarly, the nature of nanomaterials can be used to explain why SiO2 is changed from insulator to conductor.
4: macroscopic quantum tunneling effect
In recent years, some macroscopic physical quantities, such as the magnetization of microparticles, the magnetic flux in the quantum coherent devices, are also found to show the tunneling effect, which is called the macroscopic quantum tunneling effect. The quantum tunneling effect and the macroscopic quantum tunneling effect will be the future microelectricity. Sub, the basis of optoelectronic devices, or it establishes the limits of the further miniaturization of existing microelectronic devices. When microelectronic devices are further miniaturized, the above quantum effects must be taken into consideration. For example, when the semiconductor integrated circuit is manufactured, when the size of the circuit is close to the electron wavelength, the electron will overflow the device through the tunneling effect. The ultimate size of the classical circuit is about a micron level. The current developed quantum resonant tunneling transistor is a new generation of devices made of quantum effects.
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