Properties of PbS nanocrystals embedded in zirconia sol-gel film

The PbS nanocrystals (NCs) embedded in amorphous zirconia sol-gel films were grown at a temperature ranging from 200 to 350 °C. The size of PbS NCs was determined both by TEM and by the blue shift of the absorption edge, which increased with an increase of the synthesis temperature and PbS concentration in the range of 5-30 mol%. Any further increase of the PbS concentration (40-50 mol%) at 200 °C caused the separation of a thin continuous layer of bulk PbS on top of the PbS NC zirconia sol-gel film. The optical and electrical properties of the PbS NCs in the zirconia film were investigated by utilizing absorption, photoluminescence (PL) and current-voltage (I-V) measurement. The PL spectra were Stokes-shifted from the corresponding absorption edge by about 0.8 eV. The latter can be associated with the recombination processes of surface states. The I-V curves of an indium tin oxide (ITO)/PbS NCs-zirconia/Au structure exhibit nearly symmetric nonlinear behavior, while ITO/PbS NCs-zirconia/PbS bulk/Au heterostructures at room temperature exhibit a rectifying behavior with two distinct peaks, which are attributed to a resonant tunneling process via the NCs' film.