2. Why does gold become so special at the nanoscale?

2.1 Definition of a nanoparticle

Nanoparticles are defined as assemblies of atoms whose size (in all three dimensions) $x$ , $y$ and $z$ ) ranges from approximately 1 nm to 100 nm. If only two dimensions are nanometric, then we refer to them as nanowires. If only one dimension is nanometric, they are nanometric thin films. This article focuses primarily on nanoparticles (NPs). A wide variety of NP geometries can now be synthesized: nanospheres, nanocubes, nanorods, nanostars, etc. (§