How nanoparticles are made?

There are two main categories of nanofabrication: ‘Top-Down’, and ‘Bottom-Up’.  These are, respectively, destructive and constructive processes. For ‘Top-Down’ fabrication, a larger piece of the base material is systematically destroyed until the remains are at nanoscale, like chopping kindling from a tree stump. For ‘Bottom-Up’ processes, the nanoparticulates are assembled from their base atoms and molecules, like growing a tree from seed. Fabrication techniques include: atomic layer epitaxy (single-atom coatings), chemical vapor deposition (chemical reactions producing thin films), and roll-to-roll processing (stamping on ultrathin rolls of material), among many other processes.

For more details, visit https://www.nano.gov/nanotech-101/what/manufacturing or see ‘Additional Resources’ below.