Control of average size and size distribution in as-grown nanoparticle polymer composites of MSe (M = Cd or Zn)

The preparation of CdSe and ZnSe semiconductor nanoparticles in the quantum size regime (1-5 nm) within a polymer matrix is described. A carefully controlled reaction temperature and suitable choice of solvent is found to have a dramatic effect on the size of the particles produced when a soluble pyridyl polymer adduct (a polymer that contains nitrogen and dimethylcadmium or dimethylzinc) is reacted with H2Se in solution. An expected change in colour (absorbance) of the material from black through to yellow is observed for cadmium selenide and dark yellow to light yellow for zinc selenide as the particles decrease in size. TEMs reveal that cadmium selenide particles are evenly distributed in the polymer him with a size distribution wider than analogous sulfide preparations recently reported. The CdSe particles exhibit size quantization and hence a blue shift of the band edge position is observed in the absorbance and photoacoustic spectra as the reaction temperature is decreased or the polymer solubility is improved. ZnSe nanoparticle growth has been found difficult to control although a change in reaction temperature has an effect on the particle size similar to that for CdSe.