1. Small size, measured in 100s of nanometers or less
2. Unique properties because of the small size
3. Control the structure and composition on the nm scale in order to control the properties.
An area of nanotechnology that has been evolving for the last 40 years is the technique of micro- and nanolithography and etching. These techniques are the source of the great microelectronics revolution, sometimes called “top-down” nanotechnology. Here, small features are made by starting with larger materials and patterning or “carving down” to make nanoscale structures in precise patterns. Complex structures such as microprocessors containing hundreds of millions of precisely positioned nanostructures can be fabricated. Tthis is the most well-established of all forms of nanotechnology. Production machines for these techniques can cost millions of dollars and a full-scale microprocessor factory can cost a billion dollars or more. In recent years, the same “top down” nanoprocessing techniques have enabled many non-electronic applications, including micromechanical, microptical, and microfluidic devices.
“Self-Assembly” Often called molecular or chemical nanotechnology, this fundamentally different area of nanotechnology results from starting at the atomic scale and building up materials and structures, atom by atom. It is essentially molecular engineering. This is accomplished by utilizing the forces of nature to assemble nanostructures – the term “self assembly” is often used. Here the forces of chemistry are in control and we have, at least to date, somewhat less flexibility in making arbitrary structures. The nanomaterials created this way, however, have resulted in a number of consumer products. Significant advances continue, the more we explore and understand the area of chemical nanotechnology. In addition, there are many exciting applications that combine both bottom-up and top-down processing. An example of this would be single-molecule transistors that have large (macroscopic) leads fabricated by topdown as well as single molecule (microscopic) assemblies built from the bottom, up.