The role of 3-mercaptopropionic acid as a surface anchoring group and the reaction temperature
for the controlled growth of CdS crystals was investigated from a one-step aqueous synthesis
carried out both at room temperature and using a hydrothermal route. The thiol group of
3-mercaptopropionic acid forms a relatively strong bond with the cadmium atoms found at the particle
surface reducing the crystal growth rate. This leads to the formation of monodisperse crystals
of about 2 nm diameter. For a low thermal activation, at room temperature, for instance, the crystal
growth is mainly determined by the nucleation process without evidence of a large contribution
from Ostwald ripening. When the thermal activation competes with the binding energy for the thiol
group to the cadmium atom, the surface shell becomes unstable and the crystals growth involves
the coarsening mechanism. Under hydrothermal conditions the radius (r ) for the obtained crystals
follows a linear dependence for r 3 versus t (reaction time). The crystal growing process is halted
when the colloidal suspension is cooled. An appropriate control for the time and temperature of
heating allows crystals of a tailored size to be obtained. The obtained colloidal suspensions of
CdS nanocrystals were characterized from optical absorption, high-resolution transmission electron
microscopy, and photoluminescence data