STRUCTURAL AND MORPHOLOGICAL CHARACTERIZATION OF PBS NANOCRYSTALLITESSYNTHESIZED IN THE BICONTINUOUS CUBIC PHASE OF A LIPID

We report the synthesis and characterization of monodispersed lead sul fide (PbS) particles with diameters in the range 4-14 nm, using bicont inuous cubic phase as a matrix, It was found, through polarized optica l microscopy and small-angle X-ray scattering studies, that the viscou s isotropic bicontinuous cubic phase continued to exist in the ternary sodium dioctyl sulfosuccinate (AOT)/water/sodium sulfide (Na2S) syste m 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 wi thin the mesophase, A series of PbS particulate samples were synthesiz ed, using different concentrations of aqueous Na2S solutions ranging b etween 0.025 and 0.30 M, extracted from the lipid matrix and capped by thiol molecules. The structure and diameter of the particles were det ermined from X-ray diffraction studies. The particle size was found to increase linearly with increase in Na2S concentration. Transmission e lectron microscopic (TEM) characterization of monoparticulate-layer sa mples, 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 wi th no stacking fault. The monodispersity of the particles was lost for Na2S concentration >0.20 M and the larger particles showed cubic morp hology. Absorption spectra showed blue shift with decreasing size, wit h no excitonic peaks.