approach. The difference between these two approaches can be explained simply by
using an example of powder production, where chemical synthesis represents the
bottom-up approach while crushing and milling of chunks represents the equivalent
top-down process.
On examining these technologies more closely, the expression “top-down” means
starting from large pieces of material and producing the intended structure
by mechanical or chemical methods. This situation is shown schematically in
Figure 1.2. As long as the structures are within a range of sizes that are accessible
by either mechanical tools or photolithographic processes, then top-down processes
have an unmatched flexibility in their application.
Figure 1.1 A basic understanding of physics
and chemistry, and some knowledge of
materials science, is necessary to understand
the properties and behavior of nanomaterials.
As many applications are connected with
biology and medicine, some knowledge of these
areas is also required.
Figure 1.2 Conventional goods are produced via top-down processes, starting from bulk
materials. The intended product is obtained by the application of mechanical and/or chemical
processes.
2j 1 Nanomaterials: An Introduction