TABLE OF CONTENTS Many techniques, including both top-down and bottom-up approaches, have been developed and applied for the synthesis of nanoparticles. Topdown approaches include milling or attrition, repeated quenching and lithography. Attrition can produce nanoparticles ranging from a couple of tens to several hundreds nanometers in diameter. However, nanoparticles produced by attrition have a relatively broad size distribution and varied particle shape or geometry. In addition, they may contain a significant amount of impurities from the milling medium and defects resulting from milling. Such prepared nanoparticles are commonly used in the fabrication of nanocomposites and nanograined bulk materials, which require much lower sintering temperatures. In nanocomposites and nanograined bulk materials, defects may be annealed during sintering, size distribution, particle shape, and a small amount of impurities are relatively insensitive for their applications. Repeated thermal cycling may also break a bulk material into small pieces, if the material has very small thermal conductivity but a large volume change as a function of temperature. A big volume change associated with phase transition can be effectively utilized in this approach. Although very fine particles can be produced, this process is difficult to design and control so as to produce desired particle size and shape. It is also limited to materials with very poor thermal conductivity but a large volume change. Lithography, which will be discussed in Chapter 7, is another method to make small particles. [1] , [2]
Bottom-up approaches are far more popular in the synthesis of nanoparticles and many methods have been...
