In "bottom-up" the nanoparticles are used as precursors for the preparation such
as inert gas condensation, high-energy ball milling and electro deposition. These
methods can produce a very small grain size material to the nanoscale, but this
method has the downside. Specimens may contain contaminants and cavity in the
manufacturing process. There are also restrictions on the size of the pieces. As
result the applications are limited.
For the "top-down" coarse grain material is made into a fine grain material by apply
a serious force to cause a change in the microstructure of the material.
This method is called severe plastic deformation (SPD). Specimens produced by
this method have an ultra-fine grain. No particulate contamination and no cavity