Nanometals: Formation and color

Metal nanoparticles are very attractive because of their size- and shape-dependent properties. From the plethora of existing procedures for the synthesis of metal nanoparticles, the most widely used wet-chemical methods are briefly discussed, which are suitable for production of both spherical and anisometric (rod-like or prismatic) nanoparticles. The optical properties of these nanoparticles are spectacular and, therefore, have promoted a great deal of excitement during the last few decades. The basics of the origin of such optical properties are described and some of the theoretical methods accounting for them are briefly presented. Examples are shown of the color variations arising from changes in the composition, size, and shape of nanoparticles, as well as from the proximity of other metal nanoparticles.