How to make nanoscal materials?

In general, there are two approaches for the manufacture of nanoscal materials, namely; (I) top-down and (II) bottom-up methods. The top-down method refers to the uses of the traditional workshop or microfabrication method to cut, mill, and shape materials into the desired shape and order. The best known example of top-down method is lithography process. For example, a silicon wafer is coated with a layer of photoresist by spin coating technique. The photo resist-coated wafer is then prebaked to drive off excess on a hotplate. After prebaking, the photoresist is exposed to a pattern of intense light. The lithography is used to shine light on only certain parts of the wafer. Some lithography (i.e. E-beam) can provide patterns down to 10 nm. For most photoresists, the light breaks down that portion of the coating and frees it up for etching and doping. This is top-down method because it starts from a bulk materiel.

(L-side) top-down method (From http://www.nanoscience.at/aboutnano_en.html)
(R-side) bottom-up method (From http://www.impactlab.com/2008/03/31/nano-love/)

The bottom-up method refers methods that create from smaller components (usually molecular) built up into more complex assemblies. There are two fundamentally different ways of fabricating things from the bottom up (Ref. from Nanowerk).
- Self-assembly : is common throughout nature and involves components from the molecular (e.g. protein folding) to the planetary scale (e.g. weather systems) and even beyond (e.g. galaxies).
- Molecular assembly : is proposed that device is able to guide chemical reactions by positioning reactive molecules with atomic precision.
Example of bottom-up method is ZnSe nanowires grown on a ZnSe particle which appeared as a heart shape (Nanolove).