Quantum-size effects of PbS nanocrystallites in evaporated composite films

Semiconductor nanocrystallites exhibit electronic, optical and photochemical properties greatly differing from those observed in the related bulk material due to quantum size effects. In view of future applications, nanoclusters based on sulphur compounds will find great potential as photocatalysts or nonlinear optical materials. The method of interrupted island growth was applied to form PbS nanocrystallites in a dielectric SiO2 host by a two source-evaporation technology. Depending on the deposition conditions, PbS nanocrystals can be formed with grain size down to about I nm, giving a significant increase in the optical band gap from 0.41 eV for the bulk material to about 5.2 eV; XPS, XRD and TEM investigations were performed to verify the formation of PbS nanocrystallites in the SiO2 host. These nanocrystallites show an intensive photoluminescence emission band at about 435 nm, with the intensity decreasing with increasing PbS concentration. (C) 1998 Acta Metallurgica Inc.