The chemical and physical properties of thiol-stabilized semiconductor nano
crystals are reviewed. The materials prepared include cadmium and mercury c
halcogenides with sizes ranging between 1.3 and about 8 nm. In this size re
gime, the optical properties of the particles are governed by the size-quan
tization effect. All nanocrystals synthesized belong to the cubic crystal s
tructure. Some applications of this class of materials are outlined.