1、外文资料Nanotechnology and Micro-machine原文(一): Nanomaterial Nanomaterials and nanotechnology have become a magic word in modern society. Nanomaterials represent todays cutting edge in the development of novel advanced materials which promise tailor-made functionality and unheard applications in all key
2、technologies. So nanomaterials are considered as a great potential in the 21th century because of their special properties in many fields such as optics, electronics, magnetics, mechanics, and chemistry. These unique properties are attractive for various high performance applications. Examples inclu
3、de wear resistant surfaces, low temperature sinterable high-strength ceramics, and magnetic nanocomposites. Nanostructures materials present great promises and opportunities for a new generation of materials with improved and marvelous properties. It is appropriate to begin with a brief introduction
4、 to the history of the subject. Nanomaterials are found in both biological systems and man-made structures. Nature has been using nanomaterials for millions of years,as Disckson has noted: “Life itself could be regarded as a nanophase system”.Examples in which nanostructured elements play a vital ro
5、le are magnetotactic bacteria, ferritin, and molluscan teeth. Several species of aquatic bacteria use the earths magnetic field to orient thenselves. They are able to do this because they contain chains of nanosized, single-domain magnetite particles. Because they have established their orientation,
6、 they are able to swim down to nutriments and away from what is lethal to them ,oxygen. Another example of nanomaterials in nature is that herbivorous mollusks use teeth attached to a tonguelike organ, the radula, to scrape their food. These teeth have a complex structure containing nanocrystalline
7、needles. We can utilize biological templates for making nanomaterials. Apoferritin has been used as a confined reaction environment for the synthesis of nanosized magnetite particles. Some scholars consider biological nanomaterials as model systems for developing technologically useful nanomaterials
8、. Scientific work on this subject can be traced back over 100 years.In 1861 the British chemist Thomas Graham coined the term colloid to describe a solution containing 1 to 100 nm diameter particles in suspension. Around the turn of the century, such famous scientists as Rayleigh, Maxwell, and Einst
9、ein studied colloids. In 1930 the Langmuir-Blodgett method for developing monolayer films was developed. By 1960 Uyeda had used electron microscopy and diffraction to study individual particles. At about the same time, arc, plasma, and chemical flame furnaces were employed to prouduce submicron part
10、icles. Magnetic alloy particles for use in magnetic tapes were produced in 1970.By 1980, studies were made on clusters containing fewer than 100 atoms .In 1985, a team led by Smalley and Kroto found spectroscopic evidence that clusters were unusually stable. In 1991, Lijima reported studies of graph
11、itic carbon tube filaments. Research on nanomaterials has been stimulated by their technological applications. The first technological uses of these materials were as catalysts and pigments. The large surface area to volume ratio increases the chemical activity.Because of this increased activity, th
12、ere are significant cost advantages in fabricating catalysts from nanomaterials. The peoperties of some single-phase materials can be improved by preparing them as nanostructures. For example, the sintering temperature can be decreased and the plasticity increased on single-phase, structural ceramic
13、s by reducing the grain size to several nanometers. Multiphase nanostructured materials have displayed novel behavior resulting from the small size of he individual phases. Technologically useful properties of nanomaterials are not limited to their structural, chemical, or mechanical behavior. Multi
14、layers represent examples of materials in which one can modify of tune a property for a specific application by sensitively controlling the individual layer thickness. It was discovered that the resistance of Fe-Cr multilayered thin films exhibited large changes in an applied magnetic field of sever
15、al tens of kOe.This effect was given the name giant magnetoresistance (GMR). More recently, suitably annealed magnetic multilayers have been developed that exhibit significant magnetoresistance effects even in fields as low as 5 to10 Oe (Oersted). This effect may prove to be of great technological i
16、mportance for use in magnetic recording read heads. In microelectronics, the need for faster switching times and ever larger integration has motivated considerable effort to reduce the size of electronic components. Increasing the component density increases the difficulty of satisfying cooling requirements and reduces the allowable amount of energy released on switching between states. It would be ideal if the switching occurred with the mo
