Structural and morphological characterization of PbS nanocrystallites synthesized in the bicontinuous cubic phase of a lipid

We report the synthesis and characterization of monodispersed lead sulfide (PbS) particles with diameters in the range 4-14 nm, using bicontinuous cubic phase as a matrix, It was found, through polarized optical microscopy and small-angle X-ray scattering studies, that the viscous isotropic bicontinuous cubic phase continued to exist in the ternary sodium dioctyl sulfosuccinate (AOT)/water/sodium sulfide (Na2S) system as long as the concentration of aqueous Na2S solution was below 0.5 M, The exposure of this ternary mixture to aqueous 0.40 M lead nitrate (Pb(NO3)(2)) solution led to the formation of PbS nanocrystallites within the mesophase, A series of PbS particulate samples were synthesized, using different concentrations of aqueous Na2S solutions ranging between 0.025 and 0.30 M, extracted from the lipid matrix and capped by thiol molecules. The structure and diameter of the particles were determined from X-ray diffraction studies. The particle size was found to increase linearly with increase in Na2S concentration. Transmission electron microscopic (TEM) characterization of monoparticulate-layer samples, prepared by Langmuir-Blodgett technique showed PbS particles of uniform size when the concentration of Na2S solution was lower than 0.10 M. High-resolution TEM revealed the particles to be crystalline with no stacking fault. The monodispersity of the particles was lost for Na2S concentration >0.20 M and the larger particles showed cubic morphology. Absorption spectra showed blue shift with decreasing size, with no excitonic peaks.