Thermally stable nanocrystalline films of lead sulfide PbS were prepared using the chemical deposition method. The thickness of the films measured by interferometry was approximately equal to 100 nm, and the average particle size determined from the broadening of the X-ray diffraction reflections was approximately 80 nm. X-ray diffraction analysis revealed that annealing of the film at a temperature of 350°C in air results in the formation of a protective oxide sulfate phase of the composition PbO · PbSO4 on the surface of the film. It was established that the oxide sulfate phase prevents a further oxidation of the film and serves as an inhibitor of the growth of PbS nanoparticles upon heating up to a temperature of 500°C. The factors responsible for the high thermal stability of the sizes of nanoparticles and the optical properties of the PbS nanocrystalline film were discussed.
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