Approaches to Synthesis -- Bottom-up and Top-down

There are two fundamentally different approaches to synthesising nanomaterials. In the bottom-up approach, molecular components arrange themselves into progressively more complex assemblies, building up atom by atom, molecule by molecule, and cluster by cluster, starting from the smallest scale and working upward -- the chapter's example is the synthesis of nanoparticles by colloidal dispersion, where individual atoms or ions in solution gradually aggregate into nanoscale particles. In the top-down approach, by contrast, nanomaterials are synthesised by starting from bulk material and breaking it down: bulk solids are dis-assembled, mechanically or otherwise, into progressively finer pieces until what remains is constituted of only a few atoms, at the nanoscale. The two approaches reach the same nanoscale destination from opposite directions -- bottom-up by construction from smaller units, top-down by demolition of …